Question

Find the period, range, and amplitude of the cosine function.

y=-4 cos 8x

Answer 1

@jim_thompson5910 @Directrix @dan815 help?

Answer 2

what do you have so far?

Answer 3

Nothing?

Answer 4

@jim_thompson5910

Answer 5

in general, if we have y = A*cos(Bx-C) + D

we know that

|A| is the amplitude
T = 2pi/B is the period
C/B is the phase shift
y = D is the midline

Answer 6

in this problem, what is the amplitude?

Answer 7

I'm sorry, I suck at this. How do you get the amplitude?

Answer 8

compare
y = A*cos(Bx-C) + D
to
y=-4*cos(8x)

Answer 9

notice how A matches with the -4

Answer 10

|A| is the amplitude

Answer 11

So the amplitude is -4?

Answer 12

close

Answer 13

|A| = |-4| = ??

Answer 14

4?

Answer 15

Okay, the amplitude is 4, is the period 1/4 or 1/4 pi?

Answer 16

T = 2pi/B is the period

in this case, B = 8, so

T = 2pi/B
T = 2pi/8
T = pi/4

Answer 17

pi/4 is the period and that's the same as (1/4)pi

pi/4 is probably more common notation

Answer 18

what is the midline?