Question 165053
The same idea applies here as the other two questions.
 
Always isolate the radical first.  Think of the radical as a loner.
 
sqrt(a - 1) - 5 =1
 
Add 5 to both sides.
 
sqrt{a - 1} = 1 + 5
 
sqrt{a - 1} = 6
 
We now square both sides.
 
[sqrt{a - 1}]^2 = (6)^2
 
a - 1 = 36
 
Add 1 to both sides.
 
a = 36 + 1
 
a = 37
 
Go back to your original question and replace a with 37 and then simplify.
 
sqrt{a - 1} - 5 = 1....Original question
 
Let a = 37
 
sqrt{37 - 1} - 5 = 1
 
sqrt{36} - 5 = 1
 
6 - 5 = 1
 
1 = 1....It checks!
 
The answer is a = 37
 
Understand?
 
This type of equation is called a radical equation.  Later on, you will learn how to graph radical equations.