If x and y are positive and sqrtx = y, which of the following must be equal 0?

A) x-y
B) x- sqrty
C) y-2x
D) y- x^2
E) y^2 -x

Square both sides:

From there, all you need to do is subtract!

You could also plug in! Say x = 49 and y = 7. Then it’s true that the square root of x equals y, and you can try each answer choice to see which equals 0. Only E will.