What is the condition that the line y=mx+cy=mx+cy=mx+c touches the circle x2+y2=a2x^2+y^2=a^2x2+y2=a2?
c=a2(1+m2)c = a^2(1+m^2)c=a2(1+m2)
c=a(1+m2)c = a(1+m^2)c=a(1+m2)
c2=a2(1−m2)c^2 = a^2(1-m^2)c2=a2(1−m2)
c2=a2(1+m2)c^2 = a^2(1+m^2)c2=a2(1+m2)