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Given 
P(x)=3x^(4)-2x^(3)-x^(2)-12 x-4, write 
P(x) as a product of linear factors. (3.4/3.5)


P(x)=(3x+1)(x-2)(x-((-1)/(2)+(sqrt7)/(2)i))(x-((-1)/(2)-(sqrt7)/(2)i))

Given P(x)=3x42x3x212x4P(x)=3x^{4}-2x^{3}-x^{2}-12x-4, write P(x)P(x) as a product of linear factors. (33.44/33.55)\newlineP(x)=(3x+1)(x2)(x(12+72i))(x(1272i))P(x) = \left(3x + 1\right)\left(x - 2\right)\left(x - \left(-\frac{1}{2} + \frac{\sqrt{7}}{2}i\right)\right)\left(x - \left(-\frac{1}{2} - \frac{\sqrt{7}}{2}i\right)\right)

Full solution

Q. Given P(x)=3x42x3x212x4P(x)=3x^{4}-2x^{3}-x^{2}-12x-4, write P(x)P(x) as a product of linear factors. (33.44/33.55)\newlineP(x)=(3x+1)(x2)(x(12+72i))(x(1272i))P(x) = \left(3x + 1\right)\left(x - 2\right)\left(x - \left(-\frac{1}{2} + \frac{\sqrt{7}}{2}i\right)\right)\left(x - \left(-\frac{1}{2} - \frac{\sqrt{7}}{2}i\right)\right)
  1. Identify Possible Rational Roots: To factor the polynomial P(x)=3x42x3x212x4P(x)=3x^{4}-2x^{3}-x^{2}-12x-4, we first look for any rational roots using the Rational Root Theorem. The possible rational roots are the factors of the constant term 4-4 divided by the factors of the leading coefficient 33.
  2. Test x=1x=1: The factors of 4-4 are ±1\pm1, ±2\pm2, ±4\pm4, and the factors of 33 are ±1\pm1, ±3\pm3. So the possible rational roots are ±1\pm1, ±13\pm\frac{1}{3}, ±2\pm2, 4-411, ±4\pm4, 4-433. We can test these roots by direct substitution into the polynomial or by using synthetic division.
  3. Test x=1x=-1: Let's test x=1x=1: P(1)=3(1)42(1)3(1)212(1)4=321124=16P(1)=3(1)^4-2(1)^3-(1)^2-12(1)-4 = 3-2-1-12-4 = -16, which is not zero. So x=1x=1 is not a root.
  4. Test x=2x=2: Let's test x=1x=-1: P(1)=3(1)42(1)3(1)212(1)4=3+21+124=12P(-1)=3(-1)^4-2(-1)^3-(-1)^2-12(-1)-4 = 3+2-1+12-4 = 12, which is not zero. So x=1x=-1 is not a root.
  5. Perform Polynomial Division: Let's test x=2x=2: P(2)=3(2)42(2)3(2)212(2)4=3×162×84244=48164244=0P(2)=3(2)^4-2(2)^3-(2)^2-12(2)-4 = 3\times16-2\times8-4-24-4 = 48-16-4-24-4 = 0. So x=2x=2 is a root.
  6. Use Synthetic Division: Now that we have found a root, x=2x=2, we can perform polynomial division or use synthetic division to divide P(x)P(x) by (x2)(x-2) to find the other factors.
  7. Factor the Cubic Polynomial: Using synthetic division with the root x=2x=2, we divide P(x)P(x) by (x2)(x-2) and get a quotient of 3x3+4x29x23x^3+4x^2-9x-2.
  8. Test x=1x=-1: We now need to factor the cubic polynomial 3x3+4x29x23x^3+4x^2-9x-2. We can again use the Rational Root Theorem to find possible rational roots for this cubic polynomial.
  9. Test x=13x=-\frac{1}{3}: The possible rational roots for the cubic polynomial are the same as before: ±1\pm 1, ±13\pm\frac{1}{3}, ±2\pm 2, ±23\pm\frac{2}{3}, ±4\pm 4, ±43\pm\frac{4}{3}. We test these roots by direct substitution or synthetic division.
  10. Test x=13x=-\frac{1}{3}: Let's test x=1x=-1: The cubic polynomial evaluated at x=1x=-1 gives 3(1)3+4(1)29(1)2=3+4+92=83(-1)^3+4(-1)^2-9(-1)-2 = -3+4+9-2 = 8, which is not zero. So x=1x=-1 is not a root.
  11. Test x=13x=-\frac{1}{3}: Let's test x=1x=-1: The cubic polynomial evaluated at x=1x=-1 gives 3(1)3+4(1)29(1)2=3+4+92=83(-1)^3+4(-1)^2-9(-1)-2 = -3+4+9-2 = 8, which is not zero. So x=1x=-1 is not a root.Let's test x=13x=-\frac{1}{3}: The cubic polynomial evaluated at x=13x=-\frac{1}{3} gives 3(13)3+4(13)29(13)2=19+49+32=19+129189=593(-\frac{1}{3})^3+4(-\frac{1}{3})^2-9(-\frac{1}{3})-2 = -\frac{1}{9}+\frac{4}{9}+3-2 = \frac{1}{9}+\frac{12}{9}-\frac{18}{9} = -\frac{5}{9}, which is not zero. So x=13x=-\frac{1}{3} is not a root.
  12. Test x=13x=-\frac{1}{3}: Let's test x=1x=-1: The cubic polynomial evaluated at x=1x=-1 gives 3(1)3+4(1)29(1)2=3+4+92=83(-1)^3+4(-1)^2-9(-1)-2 = -3+4+9-2 = 8, which is not zero. So x=1x=-1 is not a root.Let's test x=13x=-\frac{1}{3}: The cubic polynomial evaluated at x=13x=-\frac{1}{3} gives 3(13)3+4(13)29(13)2=19+49+32=19+129189=593(-\frac{1}{3})^3+4(-\frac{1}{3})^2-9(-\frac{1}{3})-2 = -\frac{1}{9}+\frac{4}{9}+3-2 = \frac{1}{9}+\frac{12}{9}-\frac{18}{9} = -\frac{5}{9}, which is not zero. So x=13x=-\frac{1}{3} is not a root.Let's test x=13x=-\frac{1}{3} again, but this time more carefully. The cubic polynomial evaluated at x=13x=-\frac{1}{3} gives x=1x=-111, which simplifies to x=1x=-122. This is not zero, so x=13x=-\frac{1}{3} is indeed not a root.

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