Question 21Which of the following describes the set of values of $a$ for which the curves $x^2+y^2=a^2$ and $y=x^2-a$ in the real $xy$-plane intersect at exactly $3$ points?$a = \dfrac14$$\dfrac14 \lt a \lt \dfrac12$$a \gt \dfrac14$$a = \dfrac12$$a \gt \dfrac12$