# Natural Logarithms.

## Presentation on theme: "Natural Logarithms."— Presentation transcript:

Natural Logarithms

If y=ex, then ln y =x. The number e≈2.71828.
The function y=ex has an inverse, the natural logarithmic function. If y=ex, then ln y =x.

8 Simplifying Natural Logarithms Ex. Write as a single natural log.
3 ln 6 - ln 8 ln 63 - ln 8 ln 63 Use the Power Property Use the Quotient Property Enter 63/8 into the calculator 8 ln 27

Ex. Write as a single natural log. 5ln2-ln4 3lnx+lny 4ln3+4lnx
ln x3y ln 81x4

(3x+5)2=e4 (3x+5)2≈54.6 3x+5≈7.39 3x+5≈-7.39 x≈0.797 or x≈-4.130
Solving a Natural Logarithmic Equation Solve each equation ln(3x+5)2=4 Rewrite in exponential form (3x+5)2=e4 Use a calculator e4 (3x+5)2≈54.6 Take the square root of each side, use ± 3x+5≈ x+5≈-7.39 Use a calculator x≈0.797 or x≈-4.130 Solve for x. x+2 3

Solve each equation lnx=0.1 ln(3x-9)=21 ln( )=12 x=1.105 x= x+2 __ 3 x= x+2 3

Solving an Exponential Equation
Ex. Use natural logs to solve the equations 7e2x+2.5=20 7e2x=17.5 e2x=2.5 2x=ln 2.5 x=.458 Subtract 2.5 from both sides divide both sides by 7 rewrite in log form Divide both sides by 2

Ex. Use natural logs to solve the equations