# What is the right choice for question 21) ? http://postimg.org/image/p07cc10w7/

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embizze | Certified Educator

From the graph we see that tha max=3, min=-1, period is `pi` , and there is no horizontal shift (phase shift.) (We know there is no phase shift since the graph starts at the maximum at x=0 as does the cos function.)

The equation is `y=acos(b(x-h))+k` :

a: a is the amplitude `a=("max"-"min")/2=(3-(-1))/2=2`

positive as the graph is not inverted.

b: `b=(2pi)/p` where p is the period so b=2

h: h=0 as there is no phase shift

k: k is the midline `k=("max"+"min")/2=(3+(-1))/2=1`

The equation is y=2cos(2x)+1.

The answer is (a)