(x – 3) (x – 4)2 (x – 5) – 6
= (x – 3) (x – 5) (x – 4)2 – 6
= (x2 – 5x – 3x + 15) (x2 – 8x + 16) – 6
= (x2 – 8x + 15) (x2 – 8x + 16) – 6
= (m + 15) (m+ 16) – 6 … [Putting x2 – 8x = m]
= m (m + 16) + 15 (m + 16) – 6
= m2 + 16m + 15m + 240 – 6
= m2 + 31m + 234
= m2 + 18m + 13m + 234
= m(m + 18) + 13(m + 18)
= (m + 18) (m + 13)
= (x2 – 8x + 18) (x2 – 8x + 13) … [Replacing m = x2 – 8x]