Secondary 2 Maths

y is directly proportional to x^2.

Therefore, y = k x^2

When y = 60,

60 = k x^2 - (1)

When x is doubled,

y = k (2x)^2

y = 4k x^2 - (2)

Substitute your (1) into (2),

y = 4(60) = 240

It is just a simple simultaneous equation. Combine both to get your y value. Cheers!

Hi,

Understand the keywords in this type of question, like directly proportional and inversely proportional.

Next, understand the approach, like having to form equation(s) to find the unknown constant of proportionality.

Thanks.

Cheers,
Wen Shih