Question

What is the sum of the arithmetic sequence 3, 9, 15..., if there are 36 terms?

a. 3,468
b. 3,888
c. 4,234
d. 4,572

Answer 1

Answer:B✓

Explanation:

The answer is 3,888

Answer 2

we know that
the formula of the the sum of the arithmetic sequence is
Sum=n*(a1+an)/2

n=36
a1=3
a36=?

find a36
an=a1+(n-1)*d

for n=2 a2=9
9=3+(2-1)*d----> 9=3+d----> d=6
so
for n=36
a36=a1+(36-1)*6----> a36=3+35*6----> a36=213

Sum=n*(a1+an)/2-----> 36*[3+213]/2----> 3888

the answer is
3888