The equation h = 7 sine (StartFraction pi Over 21 EndFraction t) + 28 can be used to model the height, h, in feet of the end of one blade of a windmill turning on an axis above the ground as a function of time, t, in seconds. How long is the blade? Assume that the blade is pointing to the right, parallel to the ground, at t = 0, and that the windmill turns counterclockwise at a constant rate.
a 7 feet
b 14 feet
c 21 feet
d 28 feet