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Question
Factorised form of r2 – 10r + 21 is ______.
Options
(r – 1)(r – 4)
(r – 7)(r – 3)
(r – 7)(r + 3)
(r + 7)(r + 3)
Solution
Factorised form of r2 – 10r + 21 is (r – 7)(r – 3).
Explanation:
We have, r2 – 10r + 21
= r2 – 7r – 3r + 21
= r(r – 7) – 3(r – 7) ...[By splitting the middle term, so that the product of their numerical coefficients is equal constant term]
= (r – 7)(r – 3) ...[∵ x2 + (a + b)x + ab = (x + a)(x + b)]
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