几道初一数学题求解!若(x²-7xy+y²)-B＝2x²－y²,则B＝ 2. 若x&#

2019-05-07

几道初一数学题求解!

若(x²-7xy+y²)-B＝2x²－y²,则B＝
2. 若x²＋xy＝2,xy﹣y²＝7,那么x²＋y²＝

优质解答

答：
1)
(x²-7xy+y²)-B＝2x²－y²
B=(x²-7xy+y²)-(2x²－y²)=-x²-7xy+2y²
B=-x²-7xy+2y²
2)
x²＋xy＝2
xy﹣y²＝7
x²＋y²＝x²＋xy-(xy﹣y²)=2-7=-5
x²＋y²＝=-5 答：
1)
(x²-7xy+y²)-B＝2x²－y²
B=(x²-7xy+y²)-(2x²－y²)=-x²-7xy+2y²
B=-x²-7xy+2y²
2)
x²＋xy＝2
xy﹣y²＝7
x²＋y²＝x²＋xy-(xy﹣y²)=2-7=-5
x²＋y²＝=-5