We first add both 19.8 by 19.8 and therefore, that would give us 39.6.
42 - 39.6 = 2.4.
2.4 ÷ 2 = 1.2
1.2 would be the length of each sides.
Answer: 
Step-by-step explanation:
Given the following expression shown in the picture:

You need to use a process called "Ratinalization".
By definition, using Rationalization you can rewrite the expression in its simplest form so there is not Radicals in its denominator.
Then, in order to simplify the expression, you can follow the following steps:
<em>Step 1</em>. You need to multiply the numerator and the denominator of the fraction by
, which is the conjugate of the denominator
.
<em>Step 2</em>. Then you must apply the Distributive property in the numerator.
<em>Step 3</em>. You must apply the following property in the denominator:
Therefore, applying the procedure shown above, you get:

<em>Step 4</em>. You can observe that the expression can be simplified even more. Since:

You get:

M^2 + n^2
Step 1:
Substitute in the numbers
-5^2 + 3^2
Step 2:
Square both numbers
25 + 9
Step 3:
Add them together
Answer is 34
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