Question

Factorise the given expression.

q² − 10q + 21

Answer 1

q² − 10q + 21

It can be observed that, 21 = (−7) × (−3) and (−7) + (−3) = − 10

∴ q² − 10q + 21

= q² − 7q − 3q + 21

= q (q − 7) − 3 (q − 7)

= (q − 7) (q − 3)