Expand.
(a + 2)(a – 1)
(a + 2)(a – 1)= a2 + [(2)+(-1)] a + [(2)×(-1)]
{ ∵(x + p)(x + q)= x2 +(p + q)x +(p × q)
Here x = a, p = 2, q = -1 }
= a2 +(2 – 1)a +(-2)
= a2 + 2a – a – 2
= a2 + a – 2
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