d varies directly with the square of r . If d = 15 when r = 3, find d when r = 9.
A) d = 2
B) d = 135
C) d = 68
D) d = 23
E) d = 45

Question

Quizplus · Accepted Answer

The direct variation equation can be written as:

d = kr²

where k is the constant of variation.

To find k, we can use the values given in the problem:

15 = k(3²)

15 = 9k

k = 15/9

k = 5/3

Now we can use this value of k to find d when r = 9:

d = (5/3)(9²)

d = (5/3)(81)

d = 135

Therefore, the answer is B, d = 135.

D Varies Directly with the Square of R