Question

y is directly proportional to x².
It is know that y=5 for a particular value of x.
Find the value of y when x is halved.

Answer 1

y = kx^2
if you replace x with x/2, then the new y is
k(x/2)^2 = 1/4 kx^2
so the y value is divided by 4

think of the way area scales when the linear dimensions are changed.