Chapter 5 - Trigonometric Identities - Section 5.5 Double-Angle Identities - 5.5 Exercises - Page 238: 70d

$W = 200.49~sin^2~120\pi t$ $W = -100.245~cos~240\pi t+100.245$ When we graph both functions on the same coordinate axes, we can see that they are equal.

$W = 200.49~sin^2~120\pi t$ $W = -100.245~cos~240\pi t+100.245$ We can see a sketch of the graph in the window $[0,0.05]$ by $[-50,300]$ When we graph both functions on the same coordinate axes, we can see that they are equal.