Find the sum of first term of an A.P of which
the 6th term is 45 ?
Answers
Answer:
The sum of first 11 term of an A.P of which the 6th term is 45 is 495.
Answer:
Formula of nth term of AP = a_n=a+(n-1)da
n
=a+(n−1)d
where a is the first term
d is the common difference
n = No. of terms
a_na
n
= nth term
Substitute n = 6
a_6=a+(6-1)da
6
=a+(6−1)d
a_6=a+5da
6
=a+5d
6th term is 45
So, a+5d=45 --- 1
Formula of sum of first n terms =S_n=\frac{n}{2}(2a+(n-1)d)S
n
=
2
n
(2a+(n−1)d)
Substitute n = 11
S_{11}=\frac{11}{2}(2a+(11-1)d)S
11
=
2
11
(2a+(11−1)d)
S_{11}=\frac{11}{2}(2a+10d)S
11
=
2
11
(2a+10d)
S_{11}=\frac{11}{2}(2)(a+5d)S
11
=
2
11
(2)(a+5d)
Using 1
S_{11}=\frac{11}{2}(2)(45)S
11
=
2
11
(2)(45)
S_{11}=495S
11
=495
Hence the sum of first 11 term of an A.P of which the 6th term is 45 is 495
Find the sum of 32 terms of an A.P . whose 3rd term is 1 and 6th term is -11
Step-by-step explanation: