先化简,在求值1.x²-(x²+2xy-y²)+5(y²-3xy),其中x=1/
来源:学生作业帮 编辑:作业帮 分类:数学作业 时间:2024/05/07 20:50:43
先化简,在求值1.x²-(x²+2xy-y²)+5(y²-3xy),其中x=1/17,y=1/3
﹙2﹚5xy-[x²+2xy-2y²﹚],其中x=﹣2,y=﹣1
5xy-[x²+4xy-y²-(x²+2xy-2y²﹚],其中x=﹣2,y=﹣1
﹙2﹚5xy-[x²+2xy-2y²﹚],其中x=﹣2,y=﹣1
5xy-[x²+4xy-y²-(x²+2xy-2y²﹚],其中x=﹣2,y=﹣1
1.原式=.x²-(x²+2xy-y²)+5(y²-3xy)
=.x²-x²-2xy+y²+5y²-15xy
=-2xy-15xy+y²+5y²
=-17xy+6y²
=Y(-17X+6Y)
代入x=1/17,y=1/3
原式=1/3*(-17*1/17+6*1/3)
=1/3*(-1+2)
=1/3*1
=1/3
2.原式=5xy-[x²+2xy-2y²﹚],
=5xy-x²-2xy+2y²
=5xy-2xy+2y²-x²
=2y²-x²+3xy
代入:x=﹣2,y=﹣1
原式 =2*(-1)^2-(-2)^2+3*(-2)*(-1)
=2-4+6
=4
补充:5xy-[x²+4xy-y²-(x²+2xy-2y²﹚],其中x=﹣2,y=﹣1
原式=5xy-[x²+4xy-y²-x²-2xy+2y²]
=5xy-[x²-x²+4xy-2xy+2y²-y²]
=5xy-[2xy-y²]
=5xy-2xy+y²
=3xy+y²
代入x=﹣2,y=﹣1 原式=3*(-2)*(-1)+(-1)^2
=3*2+1
=6+1
=7
=.x²-x²-2xy+y²+5y²-15xy
=-2xy-15xy+y²+5y²
=-17xy+6y²
=Y(-17X+6Y)
代入x=1/17,y=1/3
原式=1/3*(-17*1/17+6*1/3)
=1/3*(-1+2)
=1/3*1
=1/3
2.原式=5xy-[x²+2xy-2y²﹚],
=5xy-x²-2xy+2y²
=5xy-2xy+2y²-x²
=2y²-x²+3xy
代入:x=﹣2,y=﹣1
原式 =2*(-1)^2-(-2)^2+3*(-2)*(-1)
=2-4+6
=4
补充:5xy-[x²+4xy-y²-(x²+2xy-2y²﹚],其中x=﹣2,y=﹣1
原式=5xy-[x²+4xy-y²-x²-2xy+2y²]
=5xy-[x²-x²+4xy-2xy+2y²-y²]
=5xy-[2xy-y²]
=5xy-2xy+y²
=3xy+y²
代入x=﹣2,y=﹣1 原式=3*(-2)*(-1)+(-1)^2
=3*2+1
=6+1
=7
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