精选问答
两道数学题,快~~~·10分~~~~~1.已知x2-xy=5,xy-y2=-3.求式子3(x2-xy-xy+y2)的值2.已知x-y=3,xy=5,则代数式(3x-4y+5xy)-(2x-3y)+5xy的值是()同学们,第一道题都没做对啊~ 我关闭问题啦~

2019-05-07

两道数学题,快~~~·10分~~~~~
1.已知x2-xy=5,xy-y2=-3.求式子3(x2-xy-xy+y2)的值
2.已知x-y=3,xy=5,则代数式(3x-4y+5xy)-(2x-3y)+5xy的值是()
同学们,第一道题都没做对啊~ 我关闭问题啦~
优质解答
1、两个式子相减:
x2-xy-(xy-y2)=5-(-3)
x2-xy-xy+y2=8
所以:3( x2-xy-xy+y2)=8×3=24
2、(3x-4y+5xy)-(2x-3y)+5xy
=3x-4y+5xy-2x+3y+5xy
=x-y+10xy
=3+10×5
=3+50
=53
1、两个式子相减:
x2-xy-(xy-y2)=5-(-3)
x2-xy-xy+y2=8
所以:3( x2-xy-xy+y2)=8×3=24
2、(3x-4y+5xy)-(2x-3y)+5xy
=3x-4y+5xy-2x+3y+5xy
=x-y+10xy
=3+10×5
=3+50
=53
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