cos^{2}x = 1 - sin²x
8(1 - sin²x) - 10sin x - 11 = 0
8 - 8sin²x - 10sin x - 11 = 0
- 8sin²x - 10sin x - 3 = 0 D = 4 sin x₁ = -3/4
sin x₂ = -1/2
x₁ = Arc sin(-3/4) = kπ+(-1)^k*arc sin(-3/4) = kπ+(-1)^k*(
-0,84806
)
x₂ = Arc sin(-1/2) = kπ+(-1)^k*arc sin(-1/2) = kπ+(-1)^k*(
-π/6
).