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Summation of Rational Expression Series

n=110(528n(n+1)(n+2))\sum_{n=1}^{10} \left( \frac{528}{n(n+1)(n+2)} \right) is equal to:

Options

A

6565

B

130130

Correct
C

220220

D

440440

Topics & Concepts

Step-by-Step Solution

To find the value of the sum: S=n=110(528n(n+1)(n+2))S = \sum_{n=1}^{10} \left( \frac{528}{n(n+1)(n+2)} \right)

We can express the general term TnT_n using partial fractions via the method of differences (telescoping series).

Notice that the numerator of the fractional part can be rewritten as: 1n(n+1)(n+2)=12[(n+2)nn(n+1)(n+2)]\frac{1}{n(n+1)(n+2)} = \frac{1}{2} \left[ \frac{(n+2) - n}{n(n+1)(n+2)} \right]

Splitting the fraction gives: 1n(n+1)(n+2)=12[1n(n+1)1(n+1)(n+2)]\frac{1}{n(n+1)(n+2)} = \frac{1}{2} \left[ \frac{1}{n(n+1)} - \frac{1}{(n+1)(n+2)} \right]

Substituting this back into the general term TnT_n: Tn=5282[1n(n+1)1(n+1)(n+2)]=264[1n(n+1)1(n+1)(n+2)]T_n = \frac{528}{2} \left[ \frac{1}{n(n+1)} - \frac{1}{(n+1)(n+2)} \right] = 264 \left[ \frac{1}{n(n+1)} - \frac{1}{(n+1)(n+2)} \right]

Now, summing TnT_n from n=1n = 1 to n=10n = 10: S=264n=110[1n(n+1)1(n+1)(n+2)]S = 264 \sum_{n=1}^{10} \left[ \frac{1}{n(n+1)} - \frac{1}{(n+1)(n+2)} \right]

Expanding the sum gives a telescoping series where intermediate terms cancel out: S=264[(112123)+(123134)++(1101111112)]S = 264 \left[ \left( \frac{1}{1 \cdot 2} - \frac{1}{2 \cdot 3} \right) + \left( \frac{1}{2 \cdot 3} - \frac{1}{3 \cdot 4} \right) + \dots + \left( \frac{1}{10 \cdot 11} - \frac{1}{11 \cdot 12} \right) \right]

All terms except the first and the last cancel out: S=264(11211112)S = 264 \left( \frac{1}{1 \cdot 2} - \frac{1}{11 \cdot 12} \right)

Simplify the expression inside the parentheses: S=264(121132)S = 264 \left( \frac{1}{2} - \frac{1}{132} \right) S=264(661132)=264(65132)S = 264 \left( \frac{66 - 1}{132} \right) = 264 \left( \frac{65}{132} \right)

Since 264132=2\frac{264}{132} = 2: S=2×65=130S = 2 \times 65 = 130

Hence, the correct option is B (130130).

Summation of Rational Expression Series | Mathematics PYQ Solution - JEE Challenger