# Thread:

1. ## tangents

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

2. 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.

3. 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.
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