3х - 15 = 0
3х = 15
х = 5
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х^2 - 2x + 4 = x^2 - 4x + 3
x^2 - 2x - x^2 + 4x = 3 - 4
2x = - 1
x = - 0,5
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y^2 - y^2+ 9 = 9
9 = 9
Корней нет
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2х^2 + 4x -30 = 0
x^2 + 2x √√- 15 = 0
D = 4 - 4(-15) = 4 + 60 = 64 √D = 8
x1 = (-2 + 8)/2 = 3
x2 = (-2 - 8)/2 = - 5
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x^2 - 6x + 9 = 0
D = 36 - 4*9 = 36 - 36 = 0 √D = 0 (только один корень)
x = (6+0) /2 = 3
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у^2 - 2y + 8 = 0
D = 4 - 4(8) = 4 - 32 = - 28 √D < 0
Корней нет