## The Number e

The number e is an important mathematical constant, around equal come 2.71828. When supplied as the base for a logarithm, we call that logarithm the natural logarithm and also write it together \\ln x.

You are watching: Is e^x always positive

### Key Takeaways

Key PointsThe herbal logarithm, created f(x) = \\ln(x), is the strength to which e have to be elevated to obtain x.The constant can be defined in plenty of ways, most of which involve calculus. For example, it is the border of the succession whose general term is (1+1 \\over n)^n. Also, it is the unique number so the the area under the curve y=1 \\over x from x=1 to x=e is 1 square unit.Key Termse: The base of the organic logarithm, 2.718281828459045…logarithm: The logarithm that a number is the exponent by which another fixed value, the base, has to be elevated to develop that number.

### The Number e

The number e, sometimes referred to as the herbal number, or Euler’s number, is an essential mathematical continuous approximately equal to 2.71828. When supplied as the base for a logarithm, the matching logarithm is called the herbal logarithm, and is created as \\ln (x). Note that \\ln (e) =1 and also that \\ln (1)=0.

There space a number of different definitions of the number e. Many of castle involve calculus. One is that e is the border of the succession whose basic term is (1+1 \\over n)^n. One more is that e is the unique number so that the area under the curve y=1/x from x=1 to x=e is 1 square unit.

Another definition of e involves the infinite collection 1+\\frac11!+\\frac12!+\\frac13!+\\frac14! +….. It have the right to be displayed that the amount of this collection is e.

### Importance of e

The number e is an extremely important in mathematics, together 0, 1, i, \\, \\textand \\, \\pi. All five of these numbers play important and recurring roles across mathematics, and also are the 5 constants showing up in the formulation that Euler’s identity, which (amazingly) claims that e^i\\pi+1=0. favor the consistent \\pi, e is irrational (it can not be composed as a proportion of integers), and it is transcendental (it is no a root of any type of non-zero polynomial through rational coefficients).

### Compound Interest

One of the countless places the number e plays a role in mathematics is in the formula for compound interest. Jacob Bernoulli uncovered this consistent by asking concerns related to the lot of money in one account after ~ a certain variety of years, if the interest is compounded n times every year. He was able to come up v the formula the if the interest rate is r percent and also is calculate n times every year, and the account originally consisted of P dollars, climate the quantity in the account after t years is offered by A=P(1+r \\over n)^nt. By climate asking about what happens as n gets arbitrarily large, he was able to come up with the formula for repetitively compounded interest, i m sorry is A=Pe^rt.

## Graphs that Exponential Functions, base e

The function f(x) = e^x is a basic exponential role with some really interesting properties.

### Key Takeaways

Key PointsThe duty f(x)=e^x is a function which is very important in calculus. It appears in numerous applications.The exponential function arises anytime a amount grows or decays at a price proportional to its current value.The graph that y=e^xlies between the graphs the y=2^x and y=3^x.Key Termstangent: A right line touching a curve at a solitary point there is no crossing it.exponential function: Any role in i m sorry an independent change is in the kind of one exponent; they are the inverse features of logarithms.asymptote: A line that a curve philosophies arbitrarily closely, as it extends towards infinity.

### Overview of e^x

The basic exponential function, occasionally referred to as the exponential function, is f(x)=e^x whereby e is the number (approximately 2.718281828) explained previously. That graph lies between the graphs that 2^x and 3^x. The graph’s y-intercept is the suggest (0,1), and it likewise contains the point (1,e). Sometimes that is written as y=\\exp (x).

The graphs that 2^x, e^x, and 3^x: The graph the y=e^x lies between that of y=2^x and y=3^x.

The graph of y=e^x is upward-sloping, and also increases much faster as x increases. The graph always lies over the x-axis, but gets arbitrary close come it for an unfavorable x; thus, the x-axis is a horizontal asymptote. The graph the e^x has the residential property that the slope of the tangent line to the graph in ~ each allude is same to that is y-coordinate at that point. y=e^x is the only role with this property.

### A model For Proportional Change

The exponential duty is supplied to model a connection in i beg your pardon a consistent change in the live independence variable offers the same proportional adjust (i. E., percentage boost or decrease) in the dependence variable. If the readjust is positive, this is referred to as exponential growth and if the is negative, it is dubbed exponential decay. For example, due to the fact that a radioactive problem decays at a rate proportional to the amount of the problem present, the amount of the substance existing at a provided time can be modeled through an exponential function. Also, due to the fact that the the development rate the a populace of bacteria in a petri dish is proportional to its size, the variety of bacteria in the food at a offered time have the right to be modeled by an exponential duty such together y=Ae^kt where A is the variety of bacteria existing initially (at time t=0) and k is a continuous called the development constant.

## Natural Logarithms

The organic logarithm is the logarithm come the basic e, where e is one irrational and also transcendental constant approximately equal to 2.718281828.

### Key Takeaways

Key PointsThe natural logarithm is the logarithm with base same to e.The number e and also the organic logarithm have plenty of applications in calculus, number theory, differential equations, complicated numbers, compound interest, and also more.Key Termsnatural logarithm: The logarithm in base e.e: The base of the organic logarithm, roughly 2.718281828459045…

### The herbal Logarithm

The logarithm that a number is the exponent by which an additional fixed value, the base, has to be elevated to develop that number. The natural logarithm is the logarithm with base same to e.

\\displaystyle \\log_e (x) = \\ln(x)

The organic logarithm have the right to be created as \\log_e x but is usually written together \\ln x. The 2 letters l and n room reversed from the order in English due to the fact that it occurs from the French (logarithm naturalle).

Just as the exponential function with base e arises naturally in plenty of calculus contexts, the organic logarithm, i m sorry is the inverse role of the exponential with base e, likewise arises in normally in plenty of contexts. That is provided much an ext frequently in physics, chemistry, and greater mathematics than various other logarithmic functions. For example, the doubling time for a population which is growing exponentially is usually offered as \\ln 2 \\over k where k is the growth rate, and also the half-life of a radioactive problem is usually provided as \\ln 2 \\over \\lambda where \\lambda is the decay constant.

### Graphing y=\\ln(x)

The role slowly grows to hopeful infinity together x increases and rapidly goes to negative infinity together x ideologies 0 (“slowly” and also “rapidly” as contrasted to any power regulation of x). The y-axis is an asymptote. The graph the the organic logarithm lies between that of y=\\log_2 x and y=\\log_3 x. Its worth at x=1 is 0, when its value at x=e is 1.

The graphs that \\log_2 x, \\ln x, and \\log_3 x: The graph that the natural logarithm lies between the basic 2 and also the basic 3 logarithms.

### Solving Equations Using \\ln(x)

The organic logarithm role can be provided to solve equations in which the change is in one exponent.

### Example: discover the optimistic root of the equation 3^x^2-1=8

The very first step is to take the organic logarithm of both sides:

​\\displaystyle \\ln (3^x^2-1) = \\ln 8

Using the power dominance of logarithms it can then be written as:

\\displaystyle (x^2-1) \\ln 3 = \\ln 8

Dividing both sides by \\ln(3) gives:

\\displaystyle x^2-1=\\ln 8 \\over \\ln 3

Thus the positive solution is x=\\sqrt\\ln 8 \\over \\ln 3 + 1.

See more: If You Make $23 Dollars An Hour Is How Much A Year ? Is$23/Hr Good?

This deserve to be calculate (approximately) with any kind of scientific handheld calculator.