tangents

• Dec 15th 2008, 08:16 AM
mxhockey140
tangents
find an equation of the line tangent to f(x)=x^2-4x at P(3,-3)
thank you
• Dec 15th 2008, 09:50 AM
chabmgph
Quote:

Originally Posted by mxhockey140
find an equation of the line tangent to f(x)=x^2-4x at P(3,-3)
thank you

Hi mxhockey,

The tangent line you are looking for has the form $y=mx+b$ where m is the same as the gradient of your function f(x) at (3, -3). So just find f'(x) and plug in x = 3 to find m.
• Dec 15th 2008, 09:53 AM
Skalkaz
Well, we seek a line crossing a given point. And tangent means "toucher" that means the slope tangent = local slope of the curve at the given point.
in the end we can calculate the local slope with usage of derivation.