 QUESTION

# Evaluate ${{(49)}^{2}}$ using the identity ${{\left( a-b \right)}^{2}}={{a}^{2}}-2ab+{{b}^{2}}$

Hint: To evaluate ${{(49)}^{2}}$ using the ${{\left( a-b \right)}^{2}}={{a}^{2}}-2ab+{{b}^{2}}$ identity write 49 as 50 - 1 , now compare and substitute the values in the given identity.

We can write ${{(49)}^{2}}$ as ${{\left( 50-1 \right)}^{2}}$
${{\left( a-b \right)}^{2}}={{a}^{2}}+{{b}^{2}}-2ab$
${{\left( 50-1 \right)}^{2}}={{50}^{2}}+{{1}^{2}}-2(50)(1)$
The value of ${{\left( 50 \right)}^{2}}$is 2500.
${{\left( 50-1 \right)}^{2}}=2500+1-100$
${{\left( 50-1 \right)}^{2}}=2501-100$
${{\left( 50-1 \right)}^{2}}=2401$
Hence the value of ${{(49)}^{2}}$ using the identity ${{\left( a-b \right)}^{2}}={{a}^{2}}-2ab+{{b}^{2}}$ is 2401.
Note: You might get confused the algebraic expansion of ${{(a-b)}^{2}}$ and${{a}^{2}}-{{b}^{2}}$ . The algebraic expansion of ${{(a-b)}^{2}}$ is ${{a}^{2}}-2ab+{{b}^{2}}$ and algebraic expansion of ${{a}^{2}}-{{b}^{2}}$ is$(a+b)(a-b)$. Both the algebraic expansions are not equal.