已知方程组5x-7y=5m+4和2x-y=3-m的解x,y的和不小于4,求m的范围。(要求有过程)
先解方程得 x=(17-12m)/9,y=(7-15m)/9x+y=(24-27m)/9>=4就锝m<=-4/9
由2X-Y=3-M得X=(3-M+Y)/2代入5X-7Y=5M+4得Y=(7-15M)/9由X+Y不小于4得[3-M+(7-15M)/9]/2+(7-15M)/9不小于4,得M小于等于44/54
答:解: x+2y=m+4.........(1) 2x+y=3m-2........(2) (1)+(2)得 3x+3y=4m+2 即:x+y= (4m+2)/3...详情>>
答:不难,很有用详情>>