已知x+y=1,x^3+3x^2+3x+3y-3y^2+y^3=37,则(x+1)+(y-1)^4=( )
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已知x+y=1,x^3+3x^2+3x+3y-3y^2+y^3=37,则(x+1)+(y-1)^4=( )
我算出了-3(x+1)(y-1)=37之后就不会算了,
我算出了-3(x+1)(y-1)=37之后就不会算了,
x^3 + y^3 = (x + y) (x^2 - xy + y^2)
= x^2 - xy + y^2
= (x + y)^2 - 3xy
= 1 - 3xy
x^2 - y^2 = (x + y) (x - y) = x - y
所以:
x^3 + 3x^2 + 3x + 3y - 3y^2 + y^3
= (x^3 + y^3) + 3(x^2 - y^2) + 3(x + y)
= 1 - 3xy + 3(x - y) + 3 = 37 ………………(楼主可能忘了前面的“1”了~)
3(-xy + x - y + 1) = 36
(x + 1) (1 - y) = 12
因为:x + y = 1,所以:1 - y = x
所以:x(x + 1) = 12
x = 3,或 x = -4
故:y = -2 ,或 y = 5
所以:
(x+1) + (y-1)^4 = 4 + (-3)^4 = 85
或:(x+1) + (y-1)^4 = -3 + 4^4 = 253
= x^2 - xy + y^2
= (x + y)^2 - 3xy
= 1 - 3xy
x^2 - y^2 = (x + y) (x - y) = x - y
所以:
x^3 + 3x^2 + 3x + 3y - 3y^2 + y^3
= (x^3 + y^3) + 3(x^2 - y^2) + 3(x + y)
= 1 - 3xy + 3(x - y) + 3 = 37 ………………(楼主可能忘了前面的“1”了~)
3(-xy + x - y + 1) = 36
(x + 1) (1 - y) = 12
因为:x + y = 1,所以:1 - y = x
所以:x(x + 1) = 12
x = 3,或 x = -4
故:y = -2 ,或 y = 5
所以:
(x+1) + (y-1)^4 = 4 + (-3)^4 = 85
或:(x+1) + (y-1)^4 = -3 + 4^4 = 253
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