Question

Cos^2x (1+tg^2a)-sin2a

Answer 1

решение:
формула tg : 1+tg^2a=1/cos^2a
${cos}^{2} a \times \frac{1}{ {cos}^{2} a} = 1 \\ 1 = {sin}^{2}a + {cos}^{2}a \\ sin2a = 2sina \times cosa \\ {sin}^{2} a + {cos}^{2} a - 2sina \times cosa = \\ ( {sina - cosa})^{2}$