The value of $\sum\limits_{n = 2}^\infty {\ln \left( {1 - \dfrac{1}{{{n^2}}}} \right)} $ equals
A.$ - \ln 3$
B.$0$
C.$ - \ln 2$
D.$ - \ln 5$
Answer
612.9k+ views
Hint: An exponent that is written in a special way is known as a logarithm. Logarithm functions are just opposite or inverse of exponential functions. We can easily express any exponential function in a logarithm form. Similarly, all the logarithm functions can be easily rewritten in exponential form. $\sum\limits_{}^{} {} $ is a mathematical letter whose meaning is ‘the sum of’. In order to solve this equation, we will have to use the properties of sigma expansion as well as of logarithm.
Complete step by step solution:
Given is $\sum\limits_{n = 2}^\infty {\ln \left( {1 - \dfrac{1}{{{n^2}}}} \right)} $
We know that according to sigma expansion and logarithm properties,
$ \Rightarrow \ln \left( {1 - \dfrac{1}{{{n^2}}}} \right) = \ln \left( {n + 1} \right) + \ln \left( {n - 1} \right) - 2\ln n$
We are given that $n = 2$ so,
$
= \ln \left( {2 + 1} \right) + \ln \left( {2 - 1} \right) - 2\ln 2 \\
= \ln 3 + \ln 1 - 2\ln 2 + \ln 4 + \ln 2 \\
= {{\ln 3}} + {{\ln 1}} - \ln 2 - {{\ln 2}} + {{\ln 4}} + {{\ln 2}} - {{\ln 3}} - {{\ln 3}} \\
= - \ln 2 \\
$
Therefore, the value of $\sum\limits_{n = 2}^\infty {\ln \left( {1 - \dfrac{1}{{{n^2}}}} \right)} $ is $ - \ln 2$.
Hence, the correct option is (C).
Note:
This problem and similar to these can very easily be solved by making use of different logarithm properties. Students should keep in mind the properties of logarithmic functions. Logarithms are useful when we want to work with large numbers. Logarithm has many uses in real life, such as in electronics, acoustics, earthquake analysis and population prediction. When the base of common logarithm is $10$ then, the base of a natural logarithm is number $e$.
Complete step by step solution:
Given is $\sum\limits_{n = 2}^\infty {\ln \left( {1 - \dfrac{1}{{{n^2}}}} \right)} $
We know that according to sigma expansion and logarithm properties,
$ \Rightarrow \ln \left( {1 - \dfrac{1}{{{n^2}}}} \right) = \ln \left( {n + 1} \right) + \ln \left( {n - 1} \right) - 2\ln n$
We are given that $n = 2$ so,
$
= \ln \left( {2 + 1} \right) + \ln \left( {2 - 1} \right) - 2\ln 2 \\
= \ln 3 + \ln 1 - 2\ln 2 + \ln 4 + \ln 2 \\
= {{\ln 3}} + {{\ln 1}} - \ln 2 - {{\ln 2}} + {{\ln 4}} + {{\ln 2}} - {{\ln 3}} - {{\ln 3}} \\
= - \ln 2 \\
$
Therefore, the value of $\sum\limits_{n = 2}^\infty {\ln \left( {1 - \dfrac{1}{{{n^2}}}} \right)} $ is $ - \ln 2$.
Hence, the correct option is (C).
Note:
This problem and similar to these can very easily be solved by making use of different logarithm properties. Students should keep in mind the properties of logarithmic functions. Logarithms are useful when we want to work with large numbers. Logarithm has many uses in real life, such as in electronics, acoustics, earthquake analysis and population prediction. When the base of common logarithm is $10$ then, the base of a natural logarithm is number $e$.
Recently Updated Pages
Write any three differences between metals and nonmetals class 10 social science CBSE

Amit standing on a horizontal plane finds a bird flying class 10 maths CBSE

Two circles of radii 5 cm and 3 cm intersect at two class 10 maths CBSE

Solve the following i John and Jivanti together have class 10 maths CBSE

What is the relation between orthocenter circumcentre class 10 maths CBSE

Two plane mirrors are inclined at 70circ A ray incident class 10 physics CBSE

Trending doubts
Explain the Treaty of Vienna of 1815 class 10 social science CBSE

Which country is known as "The land of Fire and Ice"?

1 GB equals how many MB?

10 examples of evaporation in daily life with explanations

What is the full form of POSCO class 10 social science CBSE

Make a sketch of the human nerve cell What function class 10 biology CBSE

