[" The diagonals of the parallelogram whose sides "],[ell x+my+n=0,ell x+my+n'=0,mx+ell y+n=0,mx+ell y+n'=0" include an angle."]

The diagonals of the parallelogram whose sides are lx+my+n = 0 , lx+ my+ n',=0 , mx+ly+n=0 , mx+ly+n'=0 include an angle

The diagonals of the parallelogram whose sides are lx+my+n = 0 , lx+ my+ n',=0 , mx+ly+n=0 , mx+ly+n'=0 include an angle

The diagonals of the parallelogram whose sides are lx+my+n=0,lx+my+n'=0,mx+ly+n=0,mx+ly+n'=0 include an angle

The diagonals of the parallelogram whose sides are lx+my+n=0, lx+my+n_(1)=0, mx+ly+n=0, mx+ly=n_(1)=0 include an angle

The diagonals of the parallelogram whose sides are lx+my+n=0lx+my+n',=0,mx+ly+n=0mx+ly+n'=0 include an angle

The diagonals of the parallelogram whose sides are lx+m y+n=0, l x+m y+n^(prime)=0 m x+l y+n=0, m x+l y+n^(prime)=0 include an angle

Show that the diagonals of the parallelogram whose sides are l x+m y+n=0,l x+m y+n^(prime)=0,m x+l y+n=0 and m x+l y+n^(prime)=0 include an angle pi//2 .

If the lines lx + my + n = 0, mx + ny + l = 0 and nx + ly + m = 0 are concurrent then