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Question
Expand.
(a + 2) (a − 1)
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Solution
It is known that,
(x + a) (x + b) = x2 + (a + b)x + ab
(a + 2) (a − 1) = (a)2 + {2 + (−1)}a + (2) × (−1)
= a2 + (2 − 1)a + (−2)
= a2 + 1a − 2
= a2 + a − 2
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