Question

what is the area of an issoceles right triangle whose equal side is a cm

Answer 1

It is an isosceles triangle, so both base and height are equal.
area of right triangle =
$\frac{1}{2} \times base \times height \\ = \frac{1}{2} \times a \: cm \times a \: cm\\ = \frac{1}{2} {a}^{2} \: {cm}^{2}$