constructing special angle without a protractor building special angles without a protractor

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You are watching: How to measure an angle without using a protractor

In this chapter, you will learn just how to construct, or draw, various lines, angles and shapes. You will certainly use drawing instruments, such together a ruler, to draw straight lines, a protractor to measure and also draw angles, and also a compass to draw arcs that space a certain distance indigenous a point. With the miscellaneous constructions, you will certainly investigate some of the properties of triangles and quadrilaterals; in other words, you will uncover out much more about what is always true around all or certain varieties of triangles and also quadrilaterals.

## Bisecting lines

When us construct, or draw, geometric figures, we regularly need to bisect lines or angles.Bisect way to reduced something into two equal parts. Over there are different ways come bisect a heat segment.

### Bisecting a line segment through a ruler

review through the adhering to steps.

Step 1: draw line segment ab and identify its midpoint. Step 2: Draw any line segment v the midpoint. The little marks top top AF and also FB show that AF and FB space equal.

CD is called a bisector since it bisects AB. AF = FB.

use a leader to draw and also bisect the adhering to line segments: abdominal = 6 cm and XY = 7 cm.

In great 6, you learnt how to use a compass to draw circles, and also parts that circles referred to as arcs. We can use arcs to bisect a line segment.

### Bisecting a heat segment v a compass and also ruler

Step 1

location the compass ~ above one endpoint of the line segment (point A). Attract an arc above and listed below the line. (Notice that all the clues on the arc aboveand listed below the line space the very same distance from point A.) Step 2

Without changing the compass width, ar the compass on suggest B. Draw an arc above and below the line so that the arcs overcome the an initial two. (The two points where the arcs cross room the exact same distance far from allude A and from allude B.) Step 3

use a ruler to join the points wherein the arcs intersect.This line segment (CD) is the bisector that AB. Intersect means to cross or meet.

A perpendicular is a line the meets one more line at an angle of 90°.

Notice the CD is likewise perpendicular come AB. So that is additionally called a perpendicular bisector.

job-related in your exercise book. Use a compass and a ruler to practise illustration perpendicular bisectors on heat segments.

Try this!

Work in your practice book. Use just a protractor and also ruler to attract a perpendicular bisector top top a heat segment. (Remember that we usage a protractor to measure up angles.)

## Constructing perpendicular lines

### A perpendicular heat from a given point

Step 1

Place your compass top top the given allude (point P). Draw an arc across the heat on each side of the provided point. Do not change the compass width when illustration the second arc. Step 2

From every arc on the line, draw one more arc ~ above the opposite side of the line from the given suggest (P). The two new arcs will intersect. Step 3

Use your leader to join the given allude (P) come the allude where the arcs intersect (Q). PQ is perpendicular come AB. We additionally write it favor this: PQ âŠ¥ AB.

use your compass and also ruler to attract a perpendicular line from every given point to the line segment:  ### A perpendicular line at a given allude on a line

read through the complying with steps.

Step 1

Place your compass on the given point (P). Attract an arc throughout the line on each side of the given point. Do not adjust the compass width when illustration the second arc. Step 2

Open her compass so that it is wider than the distance from among the arcs come the suggest P. Location the compass on every arc and draw an arc over or listed below the point P. The two new arcs will certainly intersect. Step 3

Use your ruler to sign up with the given suggest (P) and also the point where the arcs intersect (Q).

PQ âŠ¥ AB

usage your compass and also ruler to attract a perpendicular at the given suggest on each line: ## Bisecting angles

Angles are developed when any type of two lines meet. Us use levels (°) to measure angles.

### Measuring and classifying angles

In the figures below, every angle has actually a number native 1 come 9.

usage a protractor to measure the size of all the angles in every figure. Compose your answers on every figure.

$$\hat1 = \text_______ ^\circ$$

$$\hat1 + \hat2 = \text_______ ^\circ$$

$$\hat1 + \hat4 = \text_______ ^\circ$$

$$\hat2 + \hat3 = \text_______ ^\circ$$

$$\hat3 + \hat4 = \text_______ ^\circ$$

$$\hat1 + \hat2 + \hat4 = \text_______ ^\circ$$

$$\hat1 + \hat2 + \hat3 + \hat4 = \text_______ ^\circ$$

$$\hat6 = \text_______ ^\circ$$

$$\hat7 + \hat8 = \text_______ ^\circ$$

$$\hat6 + \hat7 + \hat8 = \text_______ ^\circ$$

$$\hat5 + \hat6 + \hat7 = \text_______ ^\circ$$

$$\hat6 + \hat5 = \text_______ ^\circ$$

$$\hat5 + \hat6 + \hat7 + \hat8 = \text_______ ^\circ$$

$$\hat5 + \hat6 + \hat7 + \hat8 + \hat9 = \text_______ ^\circ$$

alongside each price above, compose down what kind of angle it is, namely acute, obtuse, right, straight, reflex or a revolution.

### Bisecting angle without a protractor

Step 1

Place the compass ~ above the vertex of the edge (point B). Attract an arc across each eight of the angle.

Step 2

Place the compass on the suggest where one arc the cross an arm and draw an arc inside the angle. Without an altering the compass width, repeat because that the other arm so the the two arcs cross. Step 3

Use a leader to join the vertex come the point where the arcs crossing (D).

DB is the bisector that $$\hatABC$$.

usage your compass and also ruler to bisect the angle below. You could measure every of the angles through a protractor to check if you have actually bisected the provided angle correctly.

## Constructing special angles there is no a protractor

### Constructing angle of and

check out through the following steps.

Step 1

Draw a heat segment (JK). Through the compass on suggest J, attract an arc across JK and up over over point J. Step 2

Without an altering the compass width, relocate the compass come the allude where the arc crosses JK, and also draw one arc that the cross the an initial one. Step 3

Join suggest J come the suggest where the 2 arcs accomplish (point P). $$\hatPJK$$ = 60° When girlfriend learn much more about the nature of triangles later, you will recognize whythe an approach above create a 60° angle. Or can you currently work this out now? (Hint: What carry out you know around equilateral triangles?)

build an angle of 60° at allude B below. Bisect the edge you constructed. perform you notice that the bisected angle is composed of two 30° angles? expand line segment BC come A. Then measure up the angle nearby to the 60° angle.

What is its size?

The 60° angle and also its adjacent angle include up come ### Constructing angle of and

construct an edge of 90° at allude A. Go earlier to ar 10.2 if you need help. Bisect the 90° angle, to develop an edge of 45°. Go earlier to ar 10.3 if you need help.

Challenge

Work in your exercise book. Try to construct the following angles without making use of a protractor: 150°, 210° and 135°.

## Constructing triangles

In this section, you will learn how to construct triangles. Friend will need a pencil, a protractor, a ruler and a compass.

A triangle has actually three sides and also three angles. We can construct a triangle once we recognize some that its measurements, the is, that sides, the angles, or few of its sides and angles.

### Constructing triangles

Constructing triangles when three sides room given

review through the adhering to steps. They define how to construct $$\triangle ABC$$ v side lengths the 3 cm, 5 cm and 7 cm.

Step 1

Draw one side of the triangle using a ruler. It is often simpler to start with the longest side. Step 2

Set the compass broad to 5 cm. Attract an arc 5 cm away from allude A. The third vertex of the triangle will certainly be somewhere follow me this arc. Step 3

Set the compass broad to 3 cm. Draw an arc from suggest B. Note where this arc crosses the an initial arc. This will be the 3rd vertex the the triangle. Step 4

Use your ruler to join points A and also B come the allude where the arcs crossing (C). job-related in your practice book. Monitor the steps over to construct the adhering to triangles: $$\triangle ABC$$ v sides 6 cm, 7 cm and also 4 cm $$\triangle KLM$$ with sides 10 cm, 5 cm and 8 cm $$\triangle PQR$$ through sides 5 cm, 9 cm and 11 cm

Constructing triangle when specific angles and also sides room given

use the rough sketches in (a) to (c) below to construct specific triangles, making use of a ruler, compass and also protractor. Do the construction next to each rough sketch. The dotted lines show where you need to use a compass to measure up the size of a side. use a protractor to measure the size of the given angles. build $$\triangle ABC$$, v two angle and one next given. build a $$\triangle KLM$$, through two political parties andan edge given. build right-angled $$\triangle PQR$$, through thehypotenuse and also one other side given. measure the lacking angles and also sides of every triangle in 3(a) come (c) ~ above the vault page. Write the measurements at your completed constructions. compare each of your created triangles in 3(a) to (c) v a classmate"s triangles. Are the triangles specifically the same?

Challenge

construct these triangles: $$\triangle\textSTU$$, with 3 angles given: $$S = 45^\circ$$, $$T = 70^\circ$$ and $$U = 65^\circ$$ . $$\triangle\textXYZ$$, through two sides and also the angle opposite one of the sides given: $$X = 50^\circ$$ , $$XY = 8 \text cm$$ and $$XZ = 7 \text cm$$. can you find an ext than one equipment for every triangle above? explain your result to a classmate.

## Properties that triangles

The angles of a triangle have the right to be the same size or different sizes. The political parties of a triangle have the right to be the same length or various lengths.

### Properties of it is provided triangles

build $$\triangle ABC$$ next to its rough sketch below. Measure and also label the size of all its sides and angles. Measure and also write under the size of the sides and also angles of $$\triangleDEF$$ below.
Both triangle in inquiries 1 and 2 are referred to as equilateral triangles. Comment on with a classmate if the complying with is true for an it is provided triangle: all the sides space equal. all the angles room equal come 60°.

### Properties of isosceles triangles

construct $$\triangle\textDEF$$ with $$EF = 7 \textcm, ~\hatE = 50^\circ$$ and $$\hatF = 50^\circ$$.

Also construct $$\triangle\textJKL$$ with $$JK = 6 \textcm,~KL = 6 \textcm$$ and also $$\hatJ=70^\circ$$.

Measure and label every the sides and angles of every triangle. Both triangles above are referred to as isosceles triangles. Talk about with a classmate whether the following is true because that an isosceles triangle: just two sides space equal. just two angles space equal. The two equal angles are opposite the two equal sides.

### The amount of the angle in a triangle

Look at your constructed triangles $$\triangle\textABC,~\triangle\textDEF$$ and $$\triangle\textJKL$$ over and on the previous page. What is the sum of the three angles every time? walk you uncover that the amount of the internal angles of every triangle is 180°? perform the following to check if this is true for other triangles. ~ above a clean paper of paper, construct any type of triangle. Label the angles A, B and C and also cut out the triangle.
nicely tear the angles off the triangle and also fit them next to one another. an alert that $$\hatA + \hatB + \hatC = \text______^\circ$$

A square is any kind of closed form with 4 straight sides. We classify quadrilaterals according to your sides and also angles. We keep in mind which sides space parallel, perpendicular or equal. We additionally note i beg your pardon angles are equal.

Measure and also write under the size of all the angles and the lengths of every the political parties of each square below.

Square Rectangle Parallelogram Rhombus Trapezium

Kite use your answers in concern 1. Location a Ã¢ÂœÂ“ in the exactly box listed below to display which residential property is correct because that each shape.

Opposite sides space equal

All sides room equal

Two pairs of nearby sides are equal

Opposite angles are equal

All angles room equal

 Properties Parallelogram Rectangle Rhombus Square Kite Trapezium Only one pair that sides are parallel Opposite sides are parallel

### Sum that the angle in a quadrilateral

add up the 4 angles the each quadrilateral on the ahead page. What execute you an alert about the sum of the angle of every quadrilateral? go you uncover that the amount of the interior angles of each quadrilateral equates to 360°? carry out the complying with to check if this is true for various other quadrilaterals. top top a clean paper of paper, usage a ruler to construct any quadrilateral. brand the angle A, B, C and also D. Reduced out the quadrilateral. nicely tear the angle off the quadrilateral and also fit them alongside one another. What perform you notice?

You learnt exactly how to construct perpendicular currently in section 10.2. If girlfriend know just how to construct parallel lines, you should have the ability to construct any kind of quadrilateral accurately.

### Constructing parallel lines to attract quadrilaterals

review through the following steps.

Step 1

From line segment AB, note a suggest D. This allude D will certainly be on the line that will be parallel come AB. Attract a line from A with D. Step 2

Draw one arc native A that crosses advertisement and AB. Store the very same compass width and also draw an arc from suggest D together shown.

See more: Jamey Johnson You Should Have Seen It In Color, You Should Have Seen It In Color Step 3

Set the compass broad to the distance between the 2 points wherein the an initial arc crosses ad and AB. From the point where the 2nd arc the cross AD, attract a third arc to cross the second arc.