How do you factor $x^{3} + 3 x^{2} + 7 x + 21$ $x^3 + 3x^2 + 7x + 21$ ?

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Answer 1 · 2015-05-12T04:40:26

$f (x) = x^{3} + 3 x^{2} + 7 x + 21 = 0 .$ $f(x) = x^3 + 3x^2 + 7x + 21 = 0.$

Try small numbers: 1, 2, 3, -3...

f(-3) = - 27 + 27 - 21 + 21 = 0, then (x + 3) is a factor.

$f (x) = (x + 3) (x^{2} + 7)$ $f(x) = (x + 3)(x^2 + 7)$

Check: Develop $f (x) = x^{3} + 7 x + 3 x^{2} + 21 .$ $f(x) = x^3 + 7x + 3x^2 + 21.$ Correct

How do you factor x3+3x2+7x+21x^3 + 3x^2 + 7x + 21?