Solving L.H.S. of the above equation :
⇒(a−nam)m−n×(a−lan)n−l×(a−mal)l−m⇒(am−(−n))m−n×(an−(−l))n−l×(al−(−m))l−m⇒(a(m+n))m−n×(a(n+l))n−l×(a(l+m))l−m⇒a(m+n)(m−n)×a(n+l)(n−l)×a(l+m)(l−m)⇒am2−n2×an2−l2×al2−m2⇒am2−n2+n2−l2+l2−m2⇒am2−m2−n2+n2−l2+l2⇒a0⇒1.
Since, L.H.S. = R.H.S. = 1.
Hence, proved that (a−nam)m−n×(a−lan)n−l×(a−mal)l−m = 1.