Verified answer

Угол а лежит во 2 четверти, значит, sin a > 0, cos a < 0.

sin a = 9/13

cos a = -√(1 - sin^2 a) = -√(1 - 81/169) = -√(88/169) = -2√22/13

sin 2a = 2sin a*cos a = 2*9/13*(-2√22)/13 = -36√22/169