Q5 of 157 Page 30

Factorize :

m2 – 4m – 21

Given m2 – 4m – 21


Using (x + a)(x + b) = x2 + (a + b)x + ab … (I)


⇒ m2 – 4m – 21= m2 + ( – 7 + 3)m + ( – 7)×(3)


On comparing with (I),


a = – 7 and b = 3


So, m2 – 4m – 21= (m – 7)(m + 3)


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