The sum of the first 15th terms of the sequence is 320.
What is the sum of terms of an arithmetic sequence?
Arithmetic sequence is a sequence where each consequtive term has a common constant difference.
An arithmetic sequence, therefore, is defined by two parameters, viz. the starting term and the common difference.
The formula for calculating the sum of the nth term of an AP is expressed as;
Sn = n/2(2a+(n-1)d))
Given
a1 = 5
an = 145
n = 15
[tex]S_n= \dfrac{n}{2}[2a + (n-1)d ][/tex]
S15 = 15/2 {2(5) + (15-1)5}
S15 =5{10+9(6)}
S15 =5{10+54}
S15 = 5(64)
S15 = 320
Hence the sum of the first 15th terms of the sequence is 320.
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