.....................................
A21=a1+20*d
a21=-10+20*(-3)
a21=-10-60
a21=-70
2xy + x = 5
2xy + y = 6
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у - х = 1
2xy + y = 6
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у = х + 1
2х( х + 1 ) + х + 1 = 6
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у = х + 1
2хˆ2 + 3х - 5 = 0
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у1 = -1,5
х1 = -2,5
у2 = 2
х2 = 1