Step 1: Factor the denominator completely.
The given expression is:
(x−1)(x2−1)x3−x2−3x+5
We know that x2−1=(x−1)(x+1).
Substitute this into the denominator:
(x−1)(x2−1)=(x−1)(x−1)(x+1)=(x−1)2(x+1)
So the expression becomes:
(x−1)2(x+1)x3−x2−3x+5
Step 2: Check if the fraction is proper.
The degree of the numerator (x3−x2−3x+5) is 3.
The degree of the denominator ((x−1)2(x+1)=(x2−2x+1)(x+1)=x3−x2−x+1) is 3.
Since the degree of the numerator is equal to the degree of the denominator, this is an improper rational fraction. We must perform polynomial long division first.
Step 3: Perform polynomial long division.
Divide x3−x2−3x+5 by x3−x2−x+1.
x3−x2−x+1x3−x2−3x+5=1+x3−x2−x+1(x3−x2−3x+5)−(x3−x2−x+1)
=1+x3−x2−x+1−2x+4
So, the expression can be written as:
1+(x−1)2(x+1)4−2x
Step 4: Set up the partial fraction decomposition for the proper fraction.
Let f(x)=(x−1)2(x+1)4−2x.
The denominator has a repeated linear factor (x−1)2 and a distinct linear factor (x+1). The form of the partial fraction decomposition is:
(x−1)2(x+1)4−2x=x−1A+(x−1)2B+x+1C
Step 5: Clear the denominators to solve for A, B, and C.
Multiply both sides by (x−1)2(x+1):
4−2x=A(x−1)(x+1)+B(x+1)+C(x−1)2
4−2x=A(x2−1)+B(x+1)+C(x2−2x+1)
Step 6: Solve for A, B, and C by substituting convenient values for x.
• Let x=1:
4−2(1)=A(12−1)+B(1+1)+C(1−1)2
2=A(0)+B(2)+C(0)
2=2B⟹B=1
• Let x=−1:
4−2(−1)=A((−1)2−1)+B(−1+1)+C(−1−1)2
4+2=A(0)+B(0)+C(−2)2
6=4C⟹C=46=23
• Let x=0:
4−2(0)=A(02−1)+B(0+1)+C(0−1)2
4=A(−1)+B(1)+C(1)
4=−A+B+C
Substitute the values of B=1 and C=23:
4=−A+1+23
4=−A+22+23
4=−A+25
A=25−4
A=25−28
A=−23
Step 7: Write the complete partial fraction decomposition.
Substitute the values of A, B, and C back into the expression from Step 3:
1+x−1−23+(x−1)21+x+123
1−2(x−1)3+(x−1)21+2(x+1)3
The final answer is 1−2(x−1)3+(x−1)21+2(x+1)3.