Answer:
y = x²
Step-by-step explanation:
Given that y and x² are directly proportional then the equation relating them is
y = kx² ← k is the constant of proportion
When x = 2
y = k × 2² = 4k
When x = 5
y = k × 5² = 25k
Then
25k - 4k = 20 ( difference between values is 20 )
21k = 20 ( divide both sides by 21 )
k =
y = x² ← equation of proportion