# How do you find the equation of the tangent line to the graph #y=2^-x# through point (-1,2)?

##### 1 Answer

Apr 20, 2017

Use logarithmic differentiation.

Evaluate the derivative at

Use the point-slope form of the equation of the line.

#### Explanation:

Use the natural logarithm on both sides of the equation:

Use the property

Differentiate both sides:

Multiply both sides by y:

Substitute for y:

The slope, m, of the tangent line is the derivative evaluated at

Using the point-slope form of the equation of the line: