Question

30 докажите тождество sin^2 α-tg αctgα= -cos^2 α

Answer 1

cos^2 (α) - sin^2 (α) = cos (2a)

2sin^2 (α) / tg2α*tgα = (2sina*cosa) / tg2a=sin2a*cos2a/sin2a=cos2a

Answer 2

Объяснение:

1)

$\tan \alpha \times \cot \alpha = \frac{ \sin \alpha }{ \cos \alpha } \times \frac{ \cos \alpha }{ \sin \alpha } = 1$

2)

$\sin^{2} \alpha - 1 = \sin{}^{2} \alpha - ({ \sin }^{2} \alpha + \cos {}^{2} \alpha ) = \sin {}^{2} \alpha - { \sin }^{2} \alpha - { \cos }^{2} \alpha = - { \cos }^{2} \alpha$