Find the expansion of
(x + 1)(x + 4)(x + 7)
(x + 1) (x + 4) (x + 7)
we have to use the identity
(x + a)(x + b)(x + c) = x3 + (a + b + c)x2 + (ab + bc + ca)x + abc
∴ (x + 1)(x + 4)(x + 7)
= x3 + (1 + 4 + 7) x2 + (1 × 4 + 4 × 7 + 7 × 1) x + 1 × 4 × 7
= x3 + 12x2 + (4 + 28 + 7) x + 28
= x3 + 12x2 + 39x + 28
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