Tangent Lines to f(x) at Point (2,7)

[Squiller]

Homework Statement

f(x) = 4x-x²

Question: Find the equations of the lines that pass through P(2,7) and are tangent to the graph of f(x).

(P is not on f(x).)
Thats all the problem states.

Homework Equations

f(x) = 4x-x²
Point (2,7)

The Attempt at a Solution

Ive tried finding f'(x) and plugging f' into the Line equation y=mx+b.

y=(4-2x)x+b.

Then plugging in Point P.

7=(4-2x)2+b - I am not really sure if this is heading in the right direction.

 

[Defennder]

This question is very similar:
https://www.physicsforums.com/showthread.php?t=258000