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What is the number of cycles of y=9cos(θ/4+3π/2)+4 between 0 and 2π?

What is the number of cycles of y=9cos(θ/4+3π/2)+4 between 0 and 2π?-example-1
User Misiur
by
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1 Answer

10 votes

Answer: Choice C) 1/4

===================================================

Work Shown:

Let's rearrange terms a bit to say the following:


y = 9\cos\left((\theta)/(4)+(3\pi)/(2)\right)+4\\\\y = 9\cos\left((1)/(4)\theta+(3\pi)/(2)\right)+4\\\\y = 9\cos\left((1)/(4)\left(\theta+6\pi\right)\right)+4\\\\y = 9\cos\left((1)/(4)\left(\theta-(-6\pi)\right)\right)+4\\\\

The last equation is in the form
y = A\cos\left(B\left(\theta-C\right)\right)+D\\\\

where,

  • |A| = amplitude
  • B handles the period. Specifically T = 2pi/B, where T is the period
  • C handles the phase shift, aka horizontal shifting
  • D determines the midline and the vertical shifting

We only need to worry about the value of B.

In this case, B = 1/4

So,


T = (2\pi)/(B)\\\\T = 2\pi / B\\\\T = 2\pi / (1)/(4)\\\\T = 2\pi * (4)/(1)\\\\T = 8\pi\\\\

The period is 8pi. Every 8pi units, a full cycle is completed.

However, we're not going from 0 to 8pi, but instead from 0 to 2pi.

The given interval is 2pi units wide. This is (2pi)/(8pi) = 1/4 of a full cycle. This is why choice C is the answer.

User Josh David Miller
by
8.4k points
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