$r+h=a$r+h=a

$\displaystyle h-r= \frac{a}{2}$\displaystyle h-r= \frac{a}{2}

$\displaystyle r-h= \frac{a}{2}$\displaystyle r-h= \frac{a}{2}

$r^2+h^2=a^2$r^2+h^2=a^2