Question

The absoption rate of medication is an application of a special type of series, the infinite geometric series.
an=3(1/2)^(n-1) First term of the sequence is 3, and the common ratio is 1/2.
Find the sum of the first 3 terms, or S3. Either add the first three terms, or use the formula Sn=a1-a1^r^n/1-r. PLEASE HELP?!

Answer 1

it is given that a1 = 3
a2 = 3(1/2)^(2-1) = 3/2
a3= 3/4
add the first three terms
3+3/2+3/4 = 3(1+1/2+1/4) = 21/4

Answer 2

S3 = 3 (1- 1/2^3) / 1 - 1/2
= 3 * 7/8 / 1/2
= 42/8 = 21/4







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