5.
已知等式:\(\sin ^{2}5^{\circ}+\cos ^{2}35^{\circ}+\sin 5^{\circ}\cos 35^{\circ}= \dfrac {3}{4}\);\(\sin ^{2}15^{\circ}+\cos ^{2}45^{\circ}+\sin 15^{\circ}\cos 45^{\circ}= \dfrac {3}{4}\);
\(\sin ^{2}30^{\circ}+\cos ^{2}60^{\circ}+\sin 30^{\circ}\cos 60^{\circ}= \dfrac {3}{4}\);由此可归纳出对任意角度\(θ\)都成立的一个等式,并予以证明.