如果方程组x+y+=a,5x+3y=31的解x,y都是正数,求a的范围

问题描述:

如果方程组x+y+=a,5x+3y=31的解x,y都是正数,求a的范围
guocheng

1式乘以5得5x + 5y = 5a
与2式相减得,2y = 5a - 31 > 0
1式乘以3得3x + 3y = 3a
与2式相减得,2x = 31 - 3a > 0
所以31/5 < a < 31/3