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Mathematics

Using factor theorem, factorize the following:

3x3 + 2x2 - 19x + 6

Factorisation

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Answer

Let, f(x) = 3x3 + 2x2 - 19x + 6.

Substituting, x = 2 in f(x), we get :

f(2) = 3(2)3 + 2(2)2 - 19(2) + 6

= 3(8) + 2(4) - 38 + 6

= 24 + 8 - 38 + 6

= 0.

Since, f(2) = 0, thus (x - 2) is a factor of f(x).

Dividing f(x) by (x - 2), we get :

x.]3)3x2+8x3x2)3x3+2x219x+6xl3x3+6x2x2x,,,38x219xxl2fx3] +8x2+16xx2]euo[ki]x3okk 3x+6x2x,3o;llk]lmk +3x+6x2x,jok2x2k 9x×\begin{array}{l} \phantom{x -.]3)}{3x^2 + 8x - 3} \ x - 2\overline{\smash{\big)}3x^3 + 2x^2 - 19x + 6} \ \phantom{x - l}\underline{\underset{-}{}3x^3 \underset{+}{-}6x^2} \ \phantom{{x - 2}x^,,,3-}8x^2 - 19x \ \phantom{{x -l2}fx^3]\space}\underline{\underset{-}{+}8x^2 \underset{+}{-}16x} \ \phantom{{x - 2]euo[ki]}x^3okk\space}{-3x + 6} \ \phantom{{x - 2}x,'^3o;llk]lmk\space}\underline{\underset{+}{-}3x\underset{-}{+}6} \ \phantom{{x - 2}{x^,jo-k2x^2k\space}{-9x}}\times \end{array}

∴ 3x3 + 2x2 - 19x + 6 = (x - 2)(3x2 + 8x - 3)

= (x - 2)(3x2 + 9x - x - 3)

= (x - 2)[3x(x + 3) - 1(x + 3)]

= (x - 2)(3x - 1)(x + 3).

Hence, 3x3 + 2x2 − 19x + 6 = (x − 2)(3x − 1)(x + 3).

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