You are told that y is proportional to x^2 and that y=75, x=5. Find a formula for y in terms of x.

You know that y is proportional to x², so let y=kx² . You also know that y=75 and x=5. Substitute y=75 and x=5 into the equation y=kx² . Therefore: 75=k multiplied by 5². 75=25k. 75/25=k. k=3. Put k back into the original equation y=kx² . y=3x².