Question

PLEASE HELP ME!!!!!!!
y=-5cos(2x+pi/3)
On what intervals within [0, 2π) is f increasing? (Enter your answer using interval notation. If an answer does not exist, enter DNE.)

Answer 1

I think you have to take the first derivative and find where it is greater than 0.

Answer 2

i don't know how to do that(

Answer 3

Have you had calculus or what class is this question for?

Answer 4

It's Math 159 (precalculus)

Answer 5

Well then, graph it using a graphing calculator and find where the graph is rising and where it is falling.

Answer 6

http://www.wolframalpha.com/input/?i=y%3D-5cos%282x%2Bpi%2F3%29

Answer 7

I don't have a graphing calculator, unfortunately( can you see from the graph where it is increasing?

Answer 8

http://www.wolframalpha.com/input/?i=y%3D-5cos%282x%2Bpi%2F3%29+from+0+to+2Pi

Answer 9

I just don't know what points

Answer 10

So this is a normal negative cosine with period pi instead of 2pi and it has been mover pi/6 units to the left.

Answer 11

So it has its low points at -pi/6, 5pi/6, 11pi/6

Answer 12

It's high points are half way between its low points. So it has high points at 2pi/3 and 8pi/3
It is increasing between the low and the high points.

Answer 13

so the answe is [0,2pi/3] and [8pi/3,2pi)?

Answer 14

No. It increases from low point to high point.

Answer 15

low points at -pi/6, 5pi/6, 11pi/6

Answer 16

Can you graph for me please?

Answer 17

You have the wolfram graph. It is better than I could draw.

Answer 18

but it should start with o, not negative

Answer 19

Look at the one I posted

Answer 20

Witcon, thanks, but i don't know points