Question

On which of the following intervals is the function f(x) = 4 cos(2x − π) decreasing?

x = pi over 2 to x = π
x = 0 to x = pi over 2
x = pi over 2 to x = 3 pi over 2
x = π to x = 3 pi over 2

Answer 1

@Loser66

Answer 2

@IrishBoy123

Answer 3

is it C?

Answer 4

How can you get it?

Answer 5

graphing I guess?

Answer 6

ok, let see, you choose c, it means [pi/2, 3pi/2]
now plug into the original one at x = pi/2, 4 cos (2x -pi ) = 4 cos ( 2(pi/2) -pi) = 4 cos 0 = 4
next is x = 3pi/2, 4 cos (2x - pi) = 4 cos (3pi -pi) = 4 cos (2pi) = 4.
Now, a point between them: I pick pi
4cos (2x -pi) = 4 cos (2pi - pi) = 4 cos pi = -4
now you see.

Answer 7

but at pi it is -4, hence it must be down from 4 to -4