If $\sin ^6 \theta+\cos ^6 \theta=\frac{1}{3}, 0^{\circ}<\theta<90^{\circ}$, then what is the value of $\sin \theta \cos \theta$ ? |
$\frac{\sqrt{2}}{3}$ $\frac{\sqrt{6}}{6}$ $\frac{\sqrt{2}}{\sqrt{3}}$ $\frac{2}{9}$ |
$\frac{\sqrt{2}}{3}$ |
sin6 θ + cos6 θ = \(\frac{1}{3}\) (sin² θ)³ + (cos² θ)³ = \(\frac{1}{3}\) ( sin² θ + cos² θ ) . ( sin4 θ + cos4 θ - sinθ.cosθ ) = \(\frac{1}{3}\) { using , sin² θ + cos² θ = 1 } ( sin4 θ + cos4 θ - sin²θ.cos²θ ) = \(\frac{1}{3}\) ( sin² θ + cos² θ ) - sin²θ.cos²θ = \(\frac{1}{3}\) ( sin² θ + cos² θ ) - 3 sin²θ.cos²θ = \(\frac{1}{3}\) 1 - 3 sin²θ.cos²θ = \(\frac{1}{3}\) 1 - \(\frac{1}{3}\) = 3 sin²θ.cos²θ \(\frac{2}{9}\) = sin²θ.cos²θ sinθ.cosθ = \(\frac{√2}{3}\) |