已知x^2-xy=-3,2xy-y^2=-8,求代数式的值 (1)x^2+xy-y^2 (2)2x^2+4xy-3y^2
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已知x^2-xy=-3,2xy-y^2=-8,求代数式的值(1)x^2+xy-y^2(2)2x^2+4xy-3y^2已知x^2-xy=-3,2xy-y^2=-8,求代数式的值(1)x^2+xy-y^2
已知x^2-xy=-3,2xy-y^2=-8,求代数式的值 (1)x^2+xy-y^2 (2)2x^2+4xy-3y^2
已知x^2-xy=-3,2xy-y^2=-8,求代数式的值 (1)x^2+xy-y^2 (2)2x^2+4xy-3y^2
已知x^2-xy=-3,2xy-y^2=-8,求代数式的值 (1)x^2+xy-y^2 (2)2x^2+4xy-3y^2
(1)令x^2-xy=-3①
2xy-y^2=-8②
x^2+xy-y^2=①+②=-11
(2)①式两边都乘2:2x^2-2xy=-6③
②式两边都成3:6xy-3y^2=-24④
2x^2+4xy-3y^2=③+④=-30
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