Question

当k为何值时,方程组{x+y=3k-2,x-y=k 的解满足x>0,y>0？

Answer 1

x=2k-1>0 k>1/2 y=k-1>0 K>1 最终k>1

Answer 2

x+y=3k-2..............1
x-y=k...........2
1式+2式得
2x=4k-2
x=2k-1
1式-2式得
2y=2k-2
y=k-1

x=2k-1>0
k>1/2

y=k-1>0
k>1

综上k>1