Here are the solutions to the problems.
Question 8:
Split (x2+9)(x−3)x2 into partial fractions.
Step 1: Set up the partial fraction decomposition.
The denominator has an irreducible quadratic factor (x2+9) and a linear factor (x−3).
(x2+9)(x−3)x2=x2+9Ax+B+x−3C
Step 2: Multiply both sides by the common denominator (x2+9)(x−3).
x2=(Ax+B)(x−3)+C(x2+9)
Step 3: Solve for A, B, and C.
To find C, let x=3:
(3)2=(A(3)+B)(3−3)+C((3)2+9)
9=0+C(9+9)
9=18C
C=189=21
Expand the right side of the equation from Step 2:
x2=Ax2−3Ax+Bx−3B+Cx2+9C
Group terms by powers of x:
x2=(A+C)x2+(−3A+B)x+(−3B+9C)
Equate coefficients:
- Coefficient of x2: A+C=1
- Coefficient of x: −3A+B=0
- Constant term: −3B+9C=0
Substitute C=21 into equation (1):
A+21=1
A=1−21=21
Substitute A=21 into equation (2):
−3(21)+B=0
−23+B=0
B=23
(As a check, substitute B and C into equation (3): −3(23)+9(21)=−29+29=0. This is correct.)
Step 4: Substitute the values of A, B, and C back into the partial fraction form.
(x2+9)(x−3)x2=x2+921x+23+x−321
=2(x2+9)x+3+2(x−3)1
The partial fraction decomposition is 2(x2+9)x+3+2(x−3)1.
Question 9:
Split (x−1)(x2+4)1 into partial fractions.
Step 1: Set up the partial fraction decomposition.
The denominator has a linear factor (x−1) and an irreducible quadratic factor (x2+4).
(x−1)(x2+4)1=x−1A+x2+4Bx+C
Step 2: Multiply both sides by the common denominator (x−1)(x2+4).
1=A(x2+4)+(Bx+C)(x−1)
Step 3: Solve for A, B, and C.
To find A, let x=1:
1=A((1)2+4)+(B(1)+C)(1−1)
1=A(1+4)+0
1=5A
A=51
Expand the right side of the equation from Step 2:
1=Ax2+4A+Bx2−Bx+Cx−C
Group terms by powers of x:
1=(A+B)x2+(−B+C)x+(4A−C)
Equate coefficients:
- Coefficient of x2: A+B=0
- Coefficient of x: −B+C=0
- Constant term: 4A−C=1
Substitute A=51 into equation (1):
51+B=0
B=−51
Substitute B=−51 into equation (2):
−(−51)+C=0
51+C=0
C=−51
(As a check, substitute A and C into equation (3): 4(51)−(−51)=54+51=55=1. This is correct.)
Step 4: Substitute the values of A, B, and C back into the partial fraction form.
(x−1)(x2+4)1=x−151+x2+4−51x−51
=5(x−1)1−5(x2+4)x+1
The partial fraction decomposition is 5(x−1)1−5(x2+4)x+1.
Question 10:
Evaluate (B−A) if (x+3)(x+1)6x+7=x+3A+x+1B.
Step 1: Multiply both sides by the common denominator (x+3)(x+1).
6x+7=A(x+1)+B(x+3)
Step 2: Solve for A and B.
To find A, let x=−3:
6(−3)+7=A(−3+1)+B(−3+3)
−18+7=A(−2)+0
−11=−2A
A=−2−11=211
To find B, let x=−1:
6(−1)+7=A(−1+1)+B(−1+3)
−6+7=0+B(2)
1=2B
B=21
Step 3: Evaluate (B−A).
B−A=21−211
B−A=21−11
B−A=2−10
B−A=−5
The value of (B−A) is −5.