Question

Cum se transforma in produs sin18+sin72?

Answer 1

$\it sin 18^o+sin72^o=2sin\dfrac{18^o+72^o}{2}cos\dfrac{18^o-72^o}{2}=2sin45^ocos27^o=\\ \\ \\ =2\dfrac{\sqrt2}{2}cos27^o=\sqrt2cos27^o$