Answer
$a) y=\dfrac{x^2}{2}+C; b) y=\dfrac{x^3}{3}+C; c) y=\dfrac{x^4}{4}+C$
Work Step by Step
a) When $x=(\dfrac{x^2}{2})'$
This implies, $y'=x$ and $y=\dfrac{x^2}{2}+C$
b) When $x=(\dfrac{x^3}{3})'$
This implies, $y'=x^2$ and $ y=\dfrac{x^3}{3}+C$
c) When $x=(\dfrac{x^4}{4})'$
This implies, $y'=x^3$ and $ y=\dfrac{x^4}{4}+C$