Direction ratio of PQ (−3r2−3r1−6,2r2+r1+6,4r2−r1−2) Now, −3(−3r2−3r1−6)+2(2r2+r1−16)+4(4r2−r1−2)=0 ∴7r1+29r2=22‌‌−−−(1) 3(−3r2−3r1−6)−(2r2+r1−16)+(4r2−r1−2)=0 7r2+11r1=−4‌‌−−−(2)‌‌∴r1=−1,r2=1 a=−3,b=2,c=5 −a+b+‌