1) 4x+3y+10=0
2) 5x−12y+26=0
3) 7x+24y−50=0
1) l1=l26552−25a+6539+60b=0→6527a=−6599b→a=−311b
or6552+25a+6539−60b=0→6577a=6521b→a=113b
2) l1=l32520−7a+2515−24b=−4→2513a=−4+2511b→a=−13100+1311b
or2520+7a+2515+24b=0→a=2739b→a=913b
3) l2=l3325125−91a+325−300−312b=−4→a=17−325+2+17306b
or325125+91a+325−300+312b=0→a=−543b
So (a,b) ∈(0,0)