Factorise:- d² + 14d + 40
d² + 10d + 4d + 40 = 0
d(d + 10) + 4(d + 10) = 0
(d + 10)(d + 4) = 0
Either, d + 10 = 0 => d = -10 and d + 4 = 0 => d = -4
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