OliForum Matematico

Per angoli $a$ e $b$ in $[0,\pi]$, $c$ a piacere vale
$$\sin^2(b)\cos^2(c)+\big(\cos(a)\sin(b)\sin(c)-\sin(a)\cos(b)\big)^2-\big(\sin(a)+\sin(b)\big)^2 \leq 0.$$

Hint Hint grosso