O identitate trigonometrica conditionata

[Virgil Nicula]

\( \sin x + \sin^2x + \sin^3x = a\in [ - 1,3]\ \Longrightarrow\ \cos^6x- 4\cos^4x + 2(a + 3)\cos^2x = (a + 1)(3 - a) \) .

[Marius Mainea]

Avem ca \( \sin x(1+\sin^2 x)=a-\sin^2 x \)

si prin ridicare la patrat se obtine relatia dorita.