Chứng minh a) \(1 + {\tan ^2}\alpha = \frac{1}{{{\rm{co}}{{\rm{s}}^2}\alpha }}\). b) \(1 + {\cot ^2}\alpha = \frac{1}{{{\rm{si}}{{\rm{n}}^2}\alpha }}\).

Chứng minh

a) \(1 + {\tan ^2}\alpha = \frac{1}{{{\rm{co}}{{\rm{s}}^2}\alpha }}\).

b) \(1 + {\cot ^2}\alpha = \frac{1}{{{\rm{si}}{{\rm{n}}^2}\alpha }}\).