Question

find the sum of A.p 7,11,15,........12 terms , n terms?​

Answer 1

Answer:

ANSWER

As we know that, sum of n terms of an A.P. is-

S

n

=

2

n

[2a+(n−1)d]

Whereas a and d are the first term and common difference of A.P.

Given A.P.:-

7,11,15,19,.....

First term (a)=7

Common difference (d)=a

2

−a

1

=11−7=4

n=15(Given)

Therefore,

S

15

=

2

15

[2×7+(15−1)×4]

⇒S

15

=

2

15

(14+56)=

2

15

×70=525

Hence the sum of 15 terms of the given A.P. is 525.

Answer 2

Answer:

sn=n{2a+(n-1)d}/2

Step-by-step explanation:

s12= 12{14+11×4}/2

=(12×58)/2

=348

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