KCET · Maths · Indefinite Integration
\(\frac{3 x^{2}+1}{x^{2}-6 x+8}\) is equal to
- A \(3+\frac{49}{2(x-4)}-\frac{13}{2(x-2)}\)
- B \(\frac{49}{2(x-4)}-\frac{13}{2(x-2)}\)
- C \(\frac{-49}{2(x-4)}+\frac{13}{2(x-2)}\)
- D \(\frac{49}{2(x-4)}+\frac{13}{2(x-2)}\)
Answer & Solution
Correct Answer
(A) \(3+\frac{49}{2(x-4)}-\frac{13}{2(x-2)}\)
Step-by-step Solution
Detailed explanation
Given, \(\frac{3 x^{2}+1}{x^{2}-6 x+8}\)
On dividing, we get
\(\quad \frac{3 x^{2}+1}{x^{2}-6 x+8}=3+\frac{18 x-23}{x^{2}-6 x+8}\) Now, \(\frac{18 x-23}{(x-2)(x-4)}=\frac{A}{x-2}+\frac{B}{x-4}\) \(\Rightarrow \quad 18 x-23=A(x-4)+B(x-2)\) \(\Rightarrow \quad 18 x-23=(A+B) x-4 A-2 B\) Equating the coefficient of \(x\) and constant term, we get \(\quad A+B=18\) \(\quad-4 A-2 B=-23\) get
\(A+B=18\) \(-4 A-2 B=-23\) On solving these equations, we get \[ A=-\frac{13}{2}, B=\frac{49}{2} \] \(\therefore \frac{18 x-23}{(x-2)(x-4)}=-\frac{13}{2(x-2)}+\frac{49}{2(x-4)}\)
Then, from Eq. (i), we get
\[
\frac{3 x^{2}+1}{x^{2}-6 x+8}=3-\frac{13}{2(x-2)}+\frac{49}{2(x-4)}
\]
On dividing, we get
\(\quad \frac{3 x^{2}+1}{x^{2}-6 x+8}=3+\frac{18 x-23}{x^{2}-6 x+8}\) Now, \(\frac{18 x-23}{(x-2)(x-4)}=\frac{A}{x-2}+\frac{B}{x-4}\) \(\Rightarrow \quad 18 x-23=A(x-4)+B(x-2)\) \(\Rightarrow \quad 18 x-23=(A+B) x-4 A-2 B\) Equating the coefficient of \(x\) and constant term, we get \(\quad A+B=18\) \(\quad-4 A-2 B=-23\) get
\(A+B=18\) \(-4 A-2 B=-23\) On solving these equations, we get \[ A=-\frac{13}{2}, B=\frac{49}{2} \] \(\therefore \frac{18 x-23}{(x-2)(x-4)}=-\frac{13}{2(x-2)}+\frac{49}{2(x-4)}\)
Then, from Eq. (i), we get
\[
\frac{3 x^{2}+1}{x^{2}-6 x+8}=3-\frac{13}{2(x-2)}+\frac{49}{2(x-4)}
\]
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