Question

An equation of the line tangent to the graph of y=cos(2x) at x=π/4 is?

Help please?

Answer 1

Do you have a graphing calculator?

Answer 2

yes i do

Answer 3

Hold on for a minute

Answer 4

okay

Answer 5

There is a formula for this

Answer 6

and i have no clue what it is?

Answer 7

Sorry, it's called Linear Approximation

Answer 8

y - f(c) = f'(c)(x - c)

Answer 9

y - f(pi/4) = f'(pi/4)(x - pi/4)

Answer 10

If you evaluate that, you'll get your answer

Answer 11

ohhh okay... i knew there was a formula but i didn't know which one... that helps me out a lot thanks so much!

Answer 12

Make sure if you're using a calculator that you're in radians, not degrees