Correct option: D.the union of two circles and a line
d
(d)
Given in $\triangle A B C, B C$ is fixed, $A$ is variable and $A B C$ is an isosceles triangle.
Case $I$ In $\triangle A B C$,
If $\quad A B=A C$
Then, locus of $A$ is perpendicular bisector of $B C$.
$\therefore$ Locus of $A$ is a straight line.
Case $II$ When $A B=B C$
$B C$ fixed $B(a, 0), C(0, a)$, locus of $A$ is $(x-a)^2+y^2=2 a^2$, which represents the equation of circle.
Similarly, when $A C=B C$ also locus of $A$ is circle.
$\therefore$ Locus of $A$ is the union of two circles and the lines.
