Find (a + b)4 – (a – b)4. Hence, evaluate
Find (a + b)4 – (a – b)4. Hence, evaluate

NCERT Solutions for Class 11 Maths Chapter 8 Binomial Theorem Image 8

Utilizing binomial hypothesis the articulation \[\left( a\text{ }+\text{ }b \right)4\] and\[\left( a\text{ }\text{ }b \right)4\] , can be extended

\[\left( a\text{ }+\text{ }b \right)4\text{ }=\text{ }4C0\text{ }a4\text{ }+\text{ }4C1\text{ }a3\text{ }b\text{ }+\text{ }4C2\text{ }a2\text{ }b2\text{ }+\text{ }4C3\text{ }a\text{ }b3\text{ }+\text{ }4C4\text{ }b4\]

\[\left( a\text{ }\text{ }b \right)4\text{ }=\text{ }4C0\text{ }a4\text{ }\text{ }4C1\text{ }a3\text{ }b\text{ }+\text{ }4C2\text{ }a2\text{ }b2\text{ }\text{ }4C3\text{ }a\text{ }b3\text{ }+\text{ }4C4\text{ }b4\]

Presently \[\left( a\text{ }+\text{ }b \right)4\text{ }\text{ }\left( a\text{ }\text{ }b \right)4\]

\[=\text{ }4C0\text{ }a4\text{ }+\text{ }4C1\text{ }a3\text{ }b\text{ }+\text{ }4C2\text{ }a2\text{ }b2\text{ }+\text{ }4C3\text{ }a\text{ }b3\text{ }+\text{ }4C4\text{ }b4\text{ }\text{ }\left[ 4C0\text{ }a4\text{ }\text{ }4C1\text{ }a3\text{ }b\text{ }+\text{ }4C2\text{ }a2\text{ }b2\text{ }\text{ }4C3\text{ }a\text{ }b3\text{ }+\text{ }4C4\text{ }b4 \right]\]

\[=\text{ }2\text{ }\left( 4C1\text{ }a3\text{ }b\text{ }+\text{ }4C3\text{ }a\text{ }b3 \right)\]

\[=\text{ }2\text{ }\left( 4a3\text{ }b\text{ }+\text{ }4ab3 \right)\]

\[=\text{ }8ab\text{ }\left( a2\text{ }+\text{ }b2 \right)\]

Presently by subbing \[a\text{ }=\text{ }\surd 3\] and \[b\text{ }=\text{ }\surd 2\] we get

\[\left( \surd 3\text{ }+\text{ }\surd 2 \right)4\text{ }\text{ }\left( \surd 3\text{ }\text{ }\surd 2 \right)4\text{ }=\text{ }8\text{ }\left( \surd 3 \right)\text{ }\left( \surd 2 \right)\text{ }\left\{ \left( \surd 3 \right)2\text{ }+\text{ }\left( \surd 2 \right)2 \right\}\]

\[=\text{ }8\text{ }\left( \surd 6 \right)\text{ }\left( 3\text{ }+\text{ }2 \right)\] \[=\text{ }40\text{ }\surd 6\]