Дано : sin a = - 5/13 Найти : sin2 a, cos a, tg a, ctg

Sin^2 (a) = 25/169

cos^2 (a) = 1-sin^2 (a) = (169-25) / 169=144/169

cos (a) = 12/13

сos (2a) = cos^2 (a) - sin^2 (a) = (144-25) / 169=119/169

sin (2a) = 2sin (a) cos (a) = 2 * (12/13) * (-5/13) = (-120/169)

tg (a) = sin (a) / cos (a) = (-5/13) / (12/13) = (-5/12)

ctg (a) = (-12/5)

a∈ (-pi/2+2pi*n; -2pi+2pi*n), n∈Z