a) You area told that y is proportional to x2 and that when y = 75, x = 5. Find a formula for y in terms of x. y = x b) Find the value of y when x = 3. c) Find the value of x when y = 1200.

a) y is proportional to x^2, when x is 5, y is 75

Therefore: 75 = (something multiplied by) 5^2

75 = 3 x 25

Hence y = 3x^2

b) y = 3 multiplied by 3^2 

= 27

c) 1200 = 3x^2

1200/3 = x^2

400 = x^2

Undo the square of x (on both sides!)

x = 20

KM
Answered by Kezia M. Maths tutor

4150 Views

See similar Maths GCSE tutors

Related Maths GCSE answers

All answers ▸

Solve simultaneously 2x + 3y = 18 and y = 3x – 5 to find the value of x and y.


Find the value of 125^(2/3)


Calculate the gradient of this straight line


Point A (-3,5) and point B (1,-15) are to be connected to form a straight line, fing the equation of the line in the form y=mx+c?


We're here to help

contact us iconContact ustelephone icon+44 (0) 203 773 6020
Facebook logoInstagram logoLinkedIn logo

MyTutor is part of the IXL family of brands:

© 2025 by IXL Learning