Find The Sum Of The First 18 Terms Of An Arithmetic Whose General Term Is An= 3n-5

Find the sum of the first 18 terms of an Arithmetic whose general term is an= 3n-5

 

ANSWER :

The sum of 18th terms of the aritimetic sequence is 423.

STEP BY STEP EXPLANATION :

• Find the first term.

An = 3n - 5

A1 = 3(1) - 5

A1 = 3 - 5

A1 = -2

• Find the 18th term.

An = 3n - 5

A18 = 3(18) - 5

A18 = 54 - 5

A18 = 49

• Only , calculating the sum of 18th terms of the sequence.

Sn = (A1 + An) × n/2

S18 = (-2 + 49) × 18/2

S18 = 47 × 18/2

S18 = 846/2

S18 = 423

Therefore , the sum of 18th terms of the aritimetic sequence is 423.

OK.

OK.