Equation of line joining origin to the points of intersection of y=mx+1 and x2+y2=1 is x2+y2=(y−mx)2 ⇒‌‌x2+y2=y2−2mxy+m2x2 ⇒‌‌(1−m2)x2+2mxy=0 The line are perpendicular if coefficient of x2+ coefficient of y2=0 ⇒‌‌1−m2+0=0⇒m=±1