Question

Fatrorise 25a2-(9b2+42bc-4ac2)

Answer 1

Answer:

25a2 – 4b2 + 28bc – 49c2

= (5a)2 – (4b2 – 28bc + 49c2)

= (5a)2 – {(2b)2 – 2(2b)(7c) + (7c)2}

= (5a)2 – (2b – 7c)2

= (5a – 2b + 7c)(5a + 2b – 7c)