Question

what is the sum of first three term of an arithametic sequence 4,12,20​

Answer 1

Answer:

The sum of first three term of an arithmetic sequence 4,12,20 is

$4 + 12 + 20 = 36$

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Answer 2

Step-by-step explanation:

A1 = 4. D = A2-A1 = 12-4 = 8 n = 3

Sn = n/2 [2a +(n-1) d]

S3= 3/2 [2*4+(3-1)8]

S3=3/2 [8+2*8]

S3= 3/2 ( 8 +16)

S3= 3/2 *24

S3= 3+12

S3 = 15