Question

已知x的平方+xy=1,xy-y²=-4，则x²+2xy-y²=

若m²+3n-1的值为7则代数式2m²=6n+1的值为多少

Answer 1

x²+xy=1
xy-y²=-4
两式相加,得:
x²+2xy-y²=1-4=-3

m²+3n-1=7
m²+3n=8
乘2,得:
2m²+6n=16
再同时加1,得:
2m²+6n+1=17

Answer 2

x²+2xy-y²=-3……答
2m²=6n+1=6（15/12）+1=8.5……答