已知x+y=10,x^3+y^3=400,求x^2+y^2
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已知x+y=10,x^3+y^3=400,求x^2+y^2
已知x+y=10,x^3+y^3=400,求x^2+y^2
已知x+y=10,x^3+y^3=400,求x^2+y^2
x^3+y^3=(x+y)(x^2-xy+y^2)
=(x+y)[(x+y)^2-3xy]=400
10(100-3xy)=400
xy=20
x^2+y^2
=(x+y)^2-2xy
=100-40
=60
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