Solve: ${\left( {a + b} \right)^2} - {a^2} - {b^2} = $?

Hint- Here, we will be using the formula for ${\left( {a + b} \right)^2}$.As the problem depends on the algebraic identities.

As we know that ${\left( {a + b} \right)^2} = {a^2} + {b^2} + 2ab$
Using the above formula in the given expression which needs to be simplified.
$
  {\left( {a + b} \right)^2} - {a^2} - {b^2} = {a^2} + {b^2} + 2ab - {a^2} - {b^2} = 2ab \\
  \therefore {\left( {a + b} \right)^2} - {a^2} - {b^2} = 2ab \\
 $

Note- In these types of problems, the given expression which needs to be simplified is done by using some appropriate formula. In this particular problem, in the given expression ${\left( {a + b} \right)^2}$ is there so we will simply it by using the formula for ${\left( {a + b} \right)^2}$.