Question

已知方程组3x+y=1和x-2y=m的解满足x为正数,求m的取值范围

Answer 1

3x+y=1 (1)

x-2y=m (2)

(1)*2+(2),7x=2+m

x=(2+m)/7>0

m>-2

(1)-3*(2),7y=1-3m>0

m