Get Answers to all your Questions

header-bg qa

y=\frac{x^2}{(x-a)(x-b)} \text { then } \frac{d^n y}{d x^n}=

Option: 1

\frac{(-1)^{\mathrm{n}}\lfloor\mathrm{n}+1}{(\mathrm{a}-\mathrm{b})^{\mathrm{n}+1}}\left[\frac{\mathrm{a}^2}{(\mathrm{x}-\mathrm{a})^{\mathrm{n}}}-\frac{\mathrm{b}^2}{(\mathrm{x}-\mathrm{b})^{\mathrm{n}}}\right]


Option: 2

\frac{\lfloor n}{(a-b)}\left[(x-a)^n-(x-b)^n\right]


Option: 3

\frac{(-1)^{\mathrm{n}}\lfloor\mathrm{n}}{(\mathrm{a}-\mathrm{b})}\left[\frac{\mathrm{a}^2}{(\mathrm{x}-\mathrm{a})^{\mathrm{n}+1}}-\frac{\mathrm{b}^2}{(\mathrm{x}-\mathrm{b})^{\mathrm{n}+1}}\right]


Option: 4

\frac{(-1)^n\lfloor 2 n}{(a-b)^n}\left[\frac{a^2}{(x-a)^{2 n}}-\frac{b^2}{(x-b)^{2 n}}\right]


Answers (1)

best_answer

y=\frac{x^2}{(x-a)(x-b)}

Since the given fraction is not a proper one, therefore we should first divide the numerator by the denominator before resolving it into particle fractions. Here we observe orally that the quotient will be 1. so let


\begin{aligned} & \frac{x^2}{(x-a)(x-b)} \equiv 1+\frac{A}{x-a}+\frac{B}{x-b} \\ & \text { then } A=\frac{a^2}{a-b} \text { and } B=\frac{b^2}{b-a} \end{aligned}

hence,

y=1+\frac{a^2}{(a-b)(x-a)}-\frac{b^2}{(a-b)(x-b)}=1+\frac{a^2}{(a-b)(x-a)}-\frac{b^2}{(a-b)(x-b)}

Now differentiating both sides n times, we get

\mathrm{y}_{\mathrm{n}}=\frac{\mathrm{a}^2}{(\mathrm{a}-\mathrm{b})}(-1)^{\mathrm{n}} \mathrm{n} !(\mathrm{x}-\mathrm{a})^{-\mathrm{n}-1}-\frac{\mathrm{b}^2}{(\mathrm{a}-\mathrm{b})}(-1)^{\mathrm{n}} \mathrm{n} !(\mathrm{x}-\mathrm{b})^{-\mathrm{n}-1}=\frac{(-1)^{\mathrm{n}} \mathrm{n} !}{(\mathrm{a}-\mathrm{b})}\left[\frac{\mathrm{a}^2}{(\mathrm{x}-\mathrm{a})^{\mathrm{n}+1}}-\frac{\mathrm{b}^2}{(\mathrm{x}-\mathrm{b})^{\mathrm{n}+1}}\right]

 

Posted by

Rishi

View full answer

JEE Main high-scoring chapters and topics

Study 40% syllabus and score up to 100% marks in JEE