За теоремой Виета:
x1 + x2 = 7
x1*x2 = 8
2 способ
D = 7*7 - 8*4 = 49 - 32 = 17
√D = √17
x1 = (7 + √17)/2
x2 = (7 - √17)/2
x1+x2 = (7+√17)/2 + (7 - √17)/2 = 14/2 = 7
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За теоремой Виета:
x1 + x2 = 7
x1*x2 = 8
2 способ
D = 7*7 - 8*4 = 49 - 32 = 17
√D = √17
x1 = (7 + √17)/2
x2 = (7 - √17)/2
x1+x2 = (7+√17)/2 + (7 - √17)/2 = 14/2 = 7