Question

find the sum of 20terms of series2-4+6-8+10-12+.......​

Answer 1

For the general Arithmetic sequence , with terms

a , a+d , a+2d , a+3d , .................... , a + (n-1)d

where a is the 1st term and d , the common difference

The sum to n terms =

n

2

[

2

a

+

(

n

−

1

)

d

)

]

here a = 2 , d = 4-2 = 6-4 = 2 and n = 20

sum of 1st 20 terms

=

20

2

[

(

2

×

2

)

+

(

19

×

2

)

]

=

420

Answer 2

Answer:

hope this answer of mine helps you ........