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Mathematics

Using factor theorem, factorize the following:

6x3 - 7x2 - 11x + 12

Factorisation

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Answer

Let, f(x) = 6x3 - 7x2 - 11x + 12.

Substituting, x = 1 in f(x), we get :

f(1) = 6(1)3 - 7(1)2 - 11(1) + 12

= 6 - 7 - 11 + 12

= 0

Since, f(1) = 0, (x - 1) is a factor of f(x).

Dividing f(x) by (x - 1), we get :

x]3)6x2x12x1)6x37x211x+12x2l6x3+6x2x2x,,,3x211xxk.l2fx3] +x2+xx2]euo[ki]x3okk 12x+12x2x3o;llk]lmk, +12x+12x2x,jok2x2k 9x×\begin{array}{l} \phantom{x - ]3)}{6x^2 - x - 12} \ x - 1\overline{\smash{\big)}6x^3 - 7x^2 - 11x + 12} \ \phantom{x - 2l}\underline{\underset{-}{}6x^3 \underset{+}{-}6x^2} \ \phantom{{x - 2}x^,,,3-}-x^2 - 11x \ \phantom{{x -k.l2}fx^3]\space}\underline{\underset{+}{-}x^2 \underset{-}{+}x} \ \phantom{{x - 2]euo[ki]}x^3okk\space}{-12x + 12} \ \phantom{{x - 2}x^3o;llk]lmk,\space}\underline{\underset{+}{-}12x\underset{-}{+}12} \ \phantom{{x - 2}{x^,jo-k2x^2k\space}{-9x}}\times \end{array}

∴ 6x3 − 7x2 − 11x + 12 = (x − 1)(6x2 − x − 12)

= (x − 1)(6x2 − 9x + 8x − 12)

= (x − 1)[3x(2x − 3) + 4(2x − 3)]

= (x − 1)(2x − 3)(3x + 4)

Hence, 6x3 − 7x2 − 11x + 12 = (x − 1)(2x − 3)(3x + 4).

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