Find the value of AA, BB, CC, and DD for which 4x3+7x2−13x−2(x2+3)(x−1)=A+Bx+Cx2+3+Dx−1\frac{4x^3 + 7x^2 - 13x - 2}{(x^2 + 3)(x - 1)} = A + \frac{Bx + C}{x^2 + 3} + \frac{D}{x - 1}.

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Worked solution

5

1. Formulate the basic algebraic identity by multiplying throughout by the denominator.

4x3+7x2−13x−2=A(x2+3)(x−1)+(Bx+C)(x−1)+D(x2+3)4x^3 + 7x^2 - 13x - 2 = A(x^2 + 3)(x - 1) + (Bx + C)(x - 1) + D(x^2 + 3)

2. Compare the coefficients of $x^3$ to find $A$.

Comparing coefficients of x3x^3:
4=A4 = A
A=4A = 4

3. Substitute $x = 1$ to eliminate $A$, $B$, and $C$, and solve for $D$.

Let x=1x = 1:
4(1)3+7(1)2−13(1)−2=D(12+3)4(1)^3 + 7(1)^2 - 13(1) - 2 = D(1^2 + 3)
4+7−13−2=4D4 + 7 - 13 - 2 = 4D
−4=4D-4 = 4D
D=−1D = -1

4. Compare the coefficients of $x^2$ to find $B$.

Comparing coefficients of x2x^2:
7=−A+B+D7 = -A + B + D
7=−4+B−17 = -4 + B - 1
7=B−57 = B - 5
B=12B = 12

5. Substitute $x = 0$ (or compare constant terms) to find $C$.

Let x=0x = 0:
−2=A(3)(−1)+C(−1)+D(3)-2 = A(3)(-1) + C(-1) + D(3)
−2=−3A−C+3D-2 = -3A - C + 3D
−2=−3(4)−C+3(−1)-2 = -3(4) - C + 3(-1)
−2=−12−C−3-2 = -12 - C - 3
−2=−15−C-2 = -15 - C
C=−13C = -13

Answer

A=4A = 4, B=12B = 12, C=−13C = -13, D=−1D = -1

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