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Exponential Functions: (lesson 1 of 3)

Exponential Functions - Introductions

If a>0a > 0 and a1a \ne 1, then the exponential function with base a_a is given by f(x)=axf( x ) = a^x.

Natural Exponential Functions

1. The irrational number e=limx(1+1n)n2.71828e = \mathop {\lim }\limits_{x \to \infty } {\left( {1 + \frac{1}{n}} \right)^n} \approx 2.71828 \cdot \cdot \cdot or e=limx0(1+x)1xe = \mathop {\lim }\limits_{x \to 0} {\left( {1 + x} \right)^{\frac{1}{x}}}.

2. For each real xx, limx(1+xn)n=ex\mathop {\lim }\limits_{x \to \infty } {\left( {1 + \frac{x}{n}} \right)^n} = e^x.

3. f(x)=exf(x) = e^x is a natural exponential function.

Derivatives of Exponential Functions

1. ddx[ex]=ex\frac{d}{{dx}}[{e^x}] = e^x

2. ddx[ef(x)]=ef(x)f(x)\frac{d}{{dx}}[e^{f(x)}] = {e^{f(x)}} \cdot f'(x).

The hyperbolic cosine and sine functions

The hyperbolic cosine function is defined as

cosh(x)=exp(x)+exp(x)2\cosh (x) = \frac{{\exp (x) + \exp ( - x)}}{2}, <x<- \infty < x < \infty,

while the hyperbolic sine function is defined as

sin(x)=exp(x)exp(x)2\sin (x) = \frac{{\exp (x) - \exp ( - x)}}{2}, <x<- \infty < x < \infty.

Properties of hyperbolic cosine and sine functions

1. (sinh(x))=cosh(x)(\sinh (x))' = \cosh (x) , (cosh(x))=sinh(x)(\cosh (x))' = \sinh (x).

2. cosh(x)>sinh(x)\cosh (x) > \sinh (x).

3. cosh2(x)sinh2(x)=1{\cosh ^2}(x) - {\sinh ^2}(x) = 1