If m≠n and (m+n)−1 × (m−1 + n−1) = mxny, then x+y is equal to
If l,m,n are three lines such that l||m and n⊥l, prove that n⊥m.
If the diagonals of the quadrilateral formed by the lines l−1x+m1y+n1=0,l2x+m2y+n2=0,l1x+m1y+n′1=0 and (l2x+m2y+n′2=0are perpendicular,then write the value of l21−l22+m2−m22