Question & Answer
QUESTION

Find the square root of 12.25
a)3.5
b)4.25
c)4.5
d)3

ANSWER Verified Verified
Hint: In this question, we have to find the square root of a decimal number. Thus, we can try to express it in the form of the expansion of a sum of numbers i.e. in the form of ${{a}^{2}}+{{b}^{2}}+2ab$ which by the square of a sum rule would be same as ${{\left( a+b \right)}^{2}}$. Thus, in this way, we can express the number as a square of another number and thus the square root of this number would be just $\left( a+b \right)$.

Complete step-by-step answer:
The number which is given to us is 12.25. Now, we have to find the numbers a and b such that 12.25 would be the square of their sum. We note that if we take a=3 and b=0.5, then
$\begin{align}
  & {{a}^{2}}={{3}^{2}}=9 \\
 & {{b}^{2}}={{0.5}^{2}}=0.25 \\
 & 2ab=2\times 3\times 0.5=3 \\
\end{align}$
Then, by taking the sum, we obtain
${{a}^{2}}+{{b}^{2}}+2ab=9+0.25+3=12.25\text{ }.........\text{(1}\text{.1)}$
Which is the number given in the question. However, using the formula ${{a}^{2}}+{{b}^{2}}+2ab={{\left( a+b \right)}^{2}}$, we can rewrite equation (1.1) as
${{a}^{2}}+{{b}^{2}}+2ab={{\left( a+b \right)}^{2}}=12.25$
Then, by taking the square root on both sides, we obtain
$\begin{align}
  & {{\left( a+b \right)}^{2}}=12.25 \\
 & \Rightarrow \sqrt{{{\left( a+b \right)}^{2}}}=\sqrt{12.25} \\
 & \Rightarrow \sqrt{12.25}=a+b\text{ }...............\text{(1}\text{.2)} \\
\end{align}$
As in this case a=3 and b=0.5, from equation (1.1), we write can write $\sqrt{12.25}$ as
$\sqrt{12.25}=a+b=3+0.5=3.5$
Thus, we find that the square root of 12.25 is equal to 3.5 which matches option (a). Thus option (a) is the correct answer.

Note: In these types of questions, it is often easier to square the numbers given in the option and check if it matches to 12.25 as it would be a quicker method to solve the question.