Question

Find the equation of the tangent line to the curve y=4xcosx at the point (π,−4π).

I found the derivative of the function:
it's 4cosx-4xsinx.
but i don't know where to go from there.

Answer 1

thats quite easy..

Answer 2

how? it's not as if you just plug in...

Answer 3

see, you have to find the equation of a line.
you just now found the slope, and the point through which it is passing is already given..

Answer 4

that clear?

Answer 5

sort of.
i know i found the slope, but i can't seem to make an equation out of it.
i got:
(7-4pi)=(4cosx-4xsinx)(x-pi)

but i can't seem to simplify that. because we're supposed to get a number for the slope, and then for the y-intercept.

Answer 6

no no no

Answer 7

not 7, sorry, y. *

Answer 8

slope = 4cosx-4xsinx at (π,−4π)
now x = π, and y = −4π
so, slope = 4cosπ - 4πsinπ

got it?

Answer 9

now u hv value of the slope

Answer 10

OHHH, i see. thank you so much! ^^

Answer 11

you are welcome :)