11) 9х² -8х + 3 = 0
D = 64 - 108 = -44 < 0 (решений нет)
12) 9х² + х - 33 = 0
D = 1 + 1188 = 1189
√D = √1189 ≈ 34.48
x₁ = (-1 - 34.48):18 ≈ -1.97
x₂ = (-1 + 34.48):18 ≈ 1.86
13) p² + p - 90 = 0
D = 1 + 360 = 361
√D = 19
p₁ = (-1 - 19):2 = -10
p₂ = (-1 + 19):2 = 9