Question

y is inversely proportional to a*3. when y=10, a=2. a is directly proportional to x. when x=4, a=20. find the formula of y in terms of x

Answer 1

The first statement should be;

y is inversely proportional to a³.

Answer:

y = 0.64/x³

Explanation:

y is inversely proportional to a³. This is;

y ∝ 1/a³

Thus, y = k(1/a³).

Where k is the constant of proportionality.

When y = 10, a = 2.

Thus; 10 = k(1/2³)

10 = k/8

k = 80.

Thus; y = 80(1/a³) - - -(1)

Also, a is directly proportional to x. Thus;

x ∝ a

So, x = ka

when x = 4, a = 20

Thus;

4 = 20k

k = 4/20

k = 1/5

Thus;

x = a/5

a = 5x

Put 5x for a in eq 1 to get;

y = 80(1/(5x)³)

y = (80/125) × 1/x³

y = 0.64/x³