Question

помогите с тождеством

Answer 1

$(1 + {tg}^{2} \alpha ) {cos}^{4} \alpha + {sin}^{2} \alpha = 1 \\ \frac{1}{ {cos}^{2} \alpha } \times {cos}^{4} \alpha + {sin}^{2} \alpha = 1 \\ {cos}^{2} \alpha + {sin}^{2} \alpha = 1 \\ 1 = 1$