$\frac{-\sqrt{5}}{2}$

$-\sqrt{3}$

$\frac{-\sqrt{5}}{3}$

$\frac{-\sqrt{3}}{2}$

$\pm \frac{\sqrt{p^2+q^2}}{2}$

$\pm \frac{p q}{2}$

$\pm\left(\frac{p+q}{2}\right)$

$\pm \frac{\sqrt{p^2+q^2}}{4}$

$-\sin (A+B+C)$

$\cos (A+B+C)$

$\sin (A+B+C)$

$2-\cos (A+B+C)$

$\sinh ^2 x+\operatorname{coth}^2 x$

$\sinh ^2 x+\operatorname{sech}^2 x$

$\cosh ^2 x+\operatorname{sech}^2 x$

$\cosh ^2 x+\tanh ^2 x$