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Exercise 7(a) · Q2

Q.Resolve x2+1(x−1)(x−2)(x−3)\dfrac{x^2+1}{(x-1)(x-2)(x-3)} into partial fractions.

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✓ Free question

Step 1. Write

x2+1(x−1)(x−2)(x−3)=Ax−1+Bx−2+Cx−3.\frac{x^2+1}{(x-1)(x-2)(x-3)}=\frac{A}{x-1}+\frac{B}{x-2}+\frac{C}{x-3}.

Step 2. Clear denominators:

x2+1=A(x−2)(x−3)+B(x−1)(x−3)+C(x−1)(x−2).x^2+1=A(x-2)(x-3)+B(x-1)(x-3)+C(x-1)(x-2).

Step 3. Substitute x=1x=1: 1+1=A(−1)(−2) ⇒ 2=2A ⇒ A=11+1=A(-1)(-2)\ \Rightarrow\ 2=2A\ \Rightarrow\ A=1.

Step 4. Substitute x=2x=2: 4+1=B(1)(−1) ⇒ 5=−B ⇒ B=−54+1=B(1)(-1)\ \Rightarrow\ 5=-B\ \Rightarrow\ B=-5.

Step 5. Substitute x=3x=3: 9+1=C(2)(1) ⇒ 10=2C ⇒ C=59+1=C(2)(1)\ \Rightarrow\ 10=2C\ \Rightarrow\ C=5.

Step 6 (check at x=0x=0). LHS =1(−1)(−2)(−3)=−16=\dfrac{1}{(-1)(-2)(-3)}=-\dfrac16. RHS =1−1−5−2+5−3=−1+2.5−1.66‾=−16=\dfrac1{-1}-\dfrac5{-2}+\dfrac5{-3}=-1+2.5-1.6\overline{6}=-\dfrac16. They agree.

✓Final answer

x2+1(x−1)(x−2)(x−3)=1x−1−5x−2+5x−3\dfrac{x^2+1}{(x-1)(x-2)(x-3)}=\dfrac1{x-1}-\dfrac5{x-2}+\dfrac5{x-3}.

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