(x+y)^2=(x-y)^2+4xy=1+4×3=13
x+y=土√13
x^2+y^2=(x-y)^2-2xy=1-2×3=-5.(题目八成出错了.初中范围内平方不涉及到负数的,高中才涉及到)
①当x+y=√13时
x^3+y^3=(x+y)(x^2-xy+y^2)=(√13)×(-5—3)=-8√13
②放x+y=-√13时
同上可证x^3+y^3=8√13
综上所述x^3+y^3=土8√13
(2)x^2/y+y^2/x=(x^3+y^3)/xy=(土8√13)/3
(x+y)^2=(x-y)^2+4xy=1+4×3=13
x+y=土√13
x^2+y^2=(x-y)^2-2xy=1-2×3=-5.(题目八成出错了.初中范围内平方不涉及到负数的,高中才涉及到)
①当x+y=√13时
x^3+y^3=(x+y)(x^2-xy+y^2)=(√13)×(-5—3)=-8√13
②放x+y=-√13时
同上可证x^3+y^3=8√13
综上所述x^3+y^3=土8√13
(2)x^2/y+y^2/x=(x^3+y^3)/xy=(土8√13)/3