已知x²-xy=3,4xy-3y²=-5,求x²+3xy-3y²的值
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已知x²-xy=3,4xy-3y²=-5,求x²+3xy-3y²的值
已知x²-xy=3,4xy-3y²=-5,求x²+3xy-3y²的值
已知x²-xy=3,4xy-3y²=-5,求x²+3xy-3y²的值
x²+3xy-3y²
=(x²-xy)+(4xy-3y²)
=3+(-5)
=-2
两式相加,得:x²-xy+4xy-3y²=3-5
即x²+3xy-3y²=-2
x²-xy=3 4xy-3y²=-5 两者相加 等于-2