Tìm khẳng định đúng? \(c{\rm{o}}{{\rm{s}}^2}\alpha + {\sin ^2}\alpha = 1\)

A. \({\tan ^2}\alpha  + {\cot ^2}\alpha  = 1\)

B. \(c{\rm{o}}{{\rm{s}}^2}\alpha  - {\sin ^2}\alpha  = 1\)

C. \(c{\rm{o}}{{\rm{s}}^2}\alpha  + {\sin ^2}\alpha  = 1\)

D. \(c{\rm{o}}{{\rm{s}}^2}2\alpha  + {\sin ^2}2\alpha  = 2\)