Question

Y is inversely proportional to x² When x=4 y=7.5 Find y when x=5

Answer 1

Given:

• y is inversely proportional to x²
• When x = 4, y = 7.5

To find: y when x = 5

Solution:

• Given, y is inversely proportional to x².
• Then, y ∝ 1/x²
• or, y = k/x² ...(i), where k is constant of variation.

• When x = 4, y = 7.5, we get
• 7.5 = k/4²
• or, k = 7.5 × 16
• or, k = 120

• When x = 5 and k = 120, using the relation (i), we get
• y = 120/5²
• or, y = 120/25
• or, y = 4.8

Answer: when x = 5, y = 4.8 .