Prove that : (m+n)−1(m−1+n−1)=(mn)−1
L.H.S. (m+n)−1(m−1+n−1)=1m+n(1m+1n)=1m+n.n+mmn=1mn=(mn)−1=R.H.S.
Hence proved.
If l,m,n are three lines such that l||m and n⊥l, prove that n⊥m.