Show transcribed image text 20. A rectangle is inscribed in a circle of radius 5 inches. If the length of the rectangle is decreasing at the rate of 2 inches per second, how fast is the area of the rectangle changing at the instant when the length is 6 inches? 21. A spherical snowball is melting in such a manner that its radius is changing at a constant rate, decreasing from 34 cm to 18 cm in 30 minutes. At what rate, in cm per minute, is the volume of the snowball changing at the instant the radius is 6 cm? 22. A 15-foot ladder is leaning against a vertical wall. If the bottom of the ladder is being pulled away from the wall at the rate of 7 feet per second, at what rate is the area of the triangle formed by the wall, the ground, and the ladder changing, in square feet per second, at the instant the bottom of the ladder is 9 feet from the wall? 23. A 20-foot ladder is leaning against a vertical wall. If the bottom of the ladder is being pulled away from the wall at the rate of 3 feet per second, how fast is the top of the ladder dropping, in feet per second, at the instant when the bottom of the ladder is 16 feet from the wall? 24. A child standing 15 feet from the base of a lamppost casts a shadow 5 feet long. If the child is 4 feet tall and walks towards the lamppost at a speed of 10 feet per minute, at what rate, in feet per minute, will the length of his shadow be changing? Math 1431 Page 2 of 5 Section 3.1 Exercises