Question

since the equation for the tangent line is y-f(x)=f'(x)(x-a)
f(x)=2x^3 + 4x at x=4
therefore f(x)= 144
and f'(x) = 100
how do we apply this to the tangent line equation(above)? where is "a" in (x-a) ?

Answer 1

A function has many tangent lines, depending on where you want it to be tangent.

Answer 2

looking for the equation of the tangent line

Answer 3

the first equation is the general equation

Answer 4

final answer is had is 100x-256, but not sure

Answer 5

In this case \(x=4\) means use \(a=4\)

Answer 6

By the way, your equation is wrong.

The tangent line is given by \[
y-f(a) = f'(a) (x-a)
\]

Answer 7

oh, thanks

Answer 8

In this case \(a=4\)

Answer 9

So you want \[
y-f(4)=f'(4)(x-4)
\]

Answer 10

i think i got it then!