ARITHMETIC PROGRESSION A2

 

Find the sum of the 1st 22 terms of the following arithmetic progression: 5+11+17+…………………

 

Solution

 

d=6, A₁ = 5,n=22

 

S_n = n[2A₁ + (n-1)d]

       2

 

S₂₂ = 22[2(5) + (22-1)d]

        2

 

S₂₂ = 11[10 + 21d]

 

S₂₂ = 11[10 + 21(6)]       since d=6

 

S₂₂ = 11[10 + 126]  

         

S₂₂ = 110 + 1386

          

S₂₂ = 1496

 

 

Therefore the sum of 1st 22 terms is 1496.

 

TRY THIS............

 

Find the sum of the 1st 15 terms of the following arithmetic progression: 6+10+14+…………………