Question

factorise the expression b^2-4b-21​

Answer 1

Answer:

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Answer 2

$= {b}^{2} - 4b - 21 \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \\ = {b}^{2} + 3b - 7b - 21 \: \: \: \: \: \\ = b(b + 3) \: \: - 7(b - 3) \\ = (b - 7) \: \: (b + 3) \: \: \: \: \: \: \: \: \: \:$