Here's the solution for Question Q1:
Q1 a)
We need to resolve x2−x−2x−11 into partial fractions.
Step 1: Factor the denominator.
x2−x−2=(x−2)(x+1)
Step 2: Set up the partial fraction decomposition.
Since the denominator has distinct linear factors, we write:
(x−2)(x+1)x−11=x−2A+x+1B
Step 3: Combine the fractions on the right side.
(x−2)(x+1)x−11=(x−2)(x+1)A(x+1)+B(x−2)
Step 4: Equate the numerators.
x−11=A(x+1)+B(x−2)
Step 5: Solve for A and B by substituting values for x.
Let x=2:
2−11=A(2+1)+B(2−2)
−9=3A+0
A=−3
Let x=−1:
−1−11=A(−1+1)+B(−1−2)
−12=0−3B
−12=−3B
B=4
Step 6: Write the partial fraction decomposition.
x2−x−2x−11=x−2−3+x+14
The partial fraction decomposition is ∗x+14−x−23∗
Q1 b)
We need to resolve (x2+3)(x+3)3−x into partial fractions.
Step 1: Identify the types of factors in the denominator.
The denominator has an irreducible quadratic factor (x2+3) and a linear factor (x+3).
Step 2: Set up the partial fraction decomposition.
(x2+3)(x+3)3−x=x2+3Ax+B+x+3C
Step 3: Combine the fractions on the right side.
(x2+3)(x+3)3−x=(x2+3)(x+3)(Ax+B)(x+3)+C(x2+3)
Step 4: Equate the numerators.
3−x=(Ax+B)(x+3)+C(x2+3)
Step 5: Solve for A, B, and C.
Let x=−3:
3−(−3)=(A(−3)+B)(−3+3)+C((−3)2+3)
6=0+C(9+3)
6=12C
C=126=21
Expand the equation and group terms by powers of x:
3−x=Ax2+3Ax+Bx+3B+Cx2+3C
3−x=(A+C)x2+(3A+B)x+(3B+3C)
Compare coefficients:
Coefficient of x2: 0=A+C
Since C=21, then A=−21.
Coefficient of x: −1=3A+B
Substitute A=−21:
−1=3(−21)+B
−1=−23+B
B=−1+23=21
(Check constant term: 3=3B+3C=3(21)+3(21)=23+23=26=3. This is consistent.)
Step 6: Write the partial fraction decomposition.
(x2+3)(x+3)3−x=x2+3−21x+21+x+321
(x2+3)(x+3)3−x=2(x2+3)1−x+2(x+3)1
The partial fraction decomposition is ∗2(x2+3)1−x+2(x+3)1∗
Q1 c)
We need to resolve x2+x−2x3−6x+9 into partial fractions.
Step 1: Perform polynomial long division because the degree of the numerator (3) is greater than the degree of the denominator (2).
\multicolumn2rx\cline2−5x2+x−2\multicolumn2r−(x3\cline2−4\multicolumn2r0\multicolumn2r\cline3−5\multicolumn2r−1x3+x2−x2−(−x20+0x2−2x)−4x−x−3x−6x+9+2)+7+9
So, x2+x−2x3−6x+9=x−1+x2+x−2−3x+7.
Step 2: Factor the denominator of the remainder term.
x2+x−2=(x+2)(x−1)
Step 3: Set up the partial fraction decomposition for the remainder term.
(x+2)(x−1)−3x+7=x+2A+x−1B
Step 4: Combine the fractions on the right side.
(x+2)(x−1)−3x+7=(x+2)(x−1)A(x−1)+B(x+2)
Step 5: Equate the numerators.
−3x+7=A(x−1)+B(x+2)
Step 6: Solve for A and B by substituting values for x.
Let x=1:
−3(1)+7=A(1−1)+B(1+2)
4=0+3B
B=34
Let x=−2:
−3(−2)+7=A(−2−1)+B(−2+2)
6+7=−3A+0
13=−3A
A=−313
Step 7: Write the complete partial fraction decomposition.
x2+x−2x3−6x+9=x−1+x+2−313+x−134
x2+x−2x3−6x+9=x−1−3(x+2)13+3(x−1)4
The partial fraction decomposition is ∗x−1−3(x+2)13+3(x−1)4∗
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