=(2√16·4·5 -7√4·5 -√5·9)·2√5=(2·4·2√5 - 7·2√5 - 3√5)·2√5=(16√5-14√5 -3√5)×2√5= -√5·2√5= -10.
X₁ = -20
x₂ = 10
(x + 20)(x - 10) = 0
x² + 20x - 10x - 200 = 0
x² + 10x - 200 = 0 D = b²-4ac = 100 + 800 = 900 = 30²
x₁ = (-b+√D)/2a = (-10+30)/2 = 10
x₂ = (-b-√D)/2a = (-10-30)/2 = -20
Ответ: x² + 10x - 200 = 0