what $h_a$ in this triangle question.

Question

Square $PQRS$ is inscribed into $\triangle ABC$ so that vertices $P$ and $Q$ lie on sides $AB$ and $AC$ and vertices $R$ and $S$ lie on $BC$. Express the length of the square’s side through $a$ and $h_a$.

What is $h_a$?

Answer 1

Usually with $h$ we note the height of the triangle. So with $h_a$ we note the height that perpendicular to the side $a$. Usually with $a$ we note the side opposite of the vertex $A$ , i.e. the side $BC$.

But as I said it's usual math notation, but that doesn't mean it's right for you problem.