Let a, b ≠kπ : $\displaystyle a.sin\alpha a\sin\alpha +b. cos\alpha b\cos\alpha = a.sin\beta a\sin\beta +b. cos\beta b\cos\beta =c$.
Prove: cos^{2}\frac{\alpha- \cos^{2}\frac{\alpha- \beta }{2}=\frac{c^{2}}{a^{2}+b^{2}}.
Let a, b ≠kπ : $\displaystyle a.sin\alpha a\sin\alpha +b. cos\alpha b\cos\alpha = a.sin\beta a\sin\beta +b. cos\beta b\cos\beta =c$.
Prove: cos^{2}\frac{\alpha- \cos^{2}\frac{\alpha- \beta }{2}=\frac{c^{2}}{a^{2}+b^{2}}.