Answer: (4)
Step-by-step explanation:
The parts listed in the congruence statements don't correspond, so they aren't necessarily congruent.
 
        
             
        
        
        
Edited : I apologise I misunderstood the question.
You can solve the equation.
        
             
        
        
        
Answer:
a1 = 6 and an = an-1 - 5
a2 = a2-1 - 5 = a1 - 5 = 1
a3 = a3-1 - 5 = a2 - 5 = -4, etc 
Step-by-step explanation:
 
        
             
        
        
        

We have that 

, which means 

 reduces to 

 when 

, or reduces to 

 when 

.
So we can expand the summation as

Notice that the 10 contributes a total of 30 from the first sum, and -30 from the second sum, so those terms cancel, leaving us with
