Найти значение выражения (5cos 2a + 3) / (3-8cos²a)

если tg a = - √5

(5cos2α+3) / (3-8cos²α) = (5 (2cos²α-1) + 3) / (3-8cos²α) = (10cos²α-5+3) / (3-8cos²α) =

= (10cos²α-2) / (3-8cos²α)

1+tg²α=1/cos²α

1 + (-√5) ²=1+5=6

1/cos²α=6, = >cos²α=1/6

(10 * (1/6) - 2) / (3-8 * (1/6)) = (10/6-2) / (3-8/6) = (10/6-12/6) / (18/6-8/6) =

= (-2/6) / (10/6) = - 1/5=-0.2