d varies directly with the square of r . If d = 80 when r = 2, find d when r = 3.
A) d = 9
B) d = 180
C) d = 36
D) d = 60
E) d = 400

Question

Quizplus · Accepted Answer

We can use the formula for direct variation:
d = kr^2
where k is the constant of variation.
We can solve for k by substituting the given values:
80 = k(2^2)
k = 20
Now we can use this value of k to find d when r = 3:
d = 20(3^2)
d = 180
Therefore, the answer is B: d = 180.

D Varies Directly with the Square of R