Question

Find the
Sum of the first 18 terms of arithmetic sequence 3, 5, 7, 9, 11

Answer 1

Answer:

Explanation:

Given arithmetic sequence

3

,

5

,

7

,

9

,

...

...

...

,

21

The first term

a

=

3

& a common difference

d

=

5

−

3

=

7

−

5

=

⋯

=

2

If there are

n

number of terms in the above A.P. then last term

l

=

21

will be the nth term given as

l

=

a

+

(

n

−

1

)

d

21

=

3

+

(

n

−

1

)

2

n

=

10

hence the sum of given arithmetic progression (

A

.

P

.

) up to

10

terms is given general formula

S

n

=

n

2

(

a

+

l

)

S

10

=

10

2

(

3

+

21

)

=

120

Answer 2

Answer:

may be 120

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