C1:x2+y2−6x−8y−12=0 C2:x2+y2−4x+6y+k=0 Both the circles are perpendicular to each other. ∵g1=−3,f1=−4,c1=−12 g2=−2f2=3,c2=k ∵ If two circles cuts perpendicularly to each other. ⇒2g1g2+2f1f2=c1+c2 ⇒2(−3)(−2)+2(−4)(3)=−12+k ⇒12+(−24)=−12+k ⇒−12=−12+k ⇒k=0