Question

如果方程组kx-b=7 的解中,x是正数,y是负数,求k的取值范围

Answer 1

x=(7+b)/k>0

3*(7+b)/k+2ky=5

(21+3b)/k+2ky=5

2ky=5-(21+3b)/k

y=(5-(21+3b)/k)/2k-7 k>0 kk>0

bk>(21+3b)/5