Question

2. (i) Find the sum of 20 terms of series 2 - 4 + 6 - 8 + 10 - 12 +
+ ..​

Answer 1

Answer:

-20

Step-by-step explanation:

Number series : 2 - 4 + 6 - 8 + 10 - 12 +

1) Pair two terms together

2) We are finding the sum of 10 pairs

Find the sum of every pair:

2 - 4 = -2

6 - 8 = -2

Every pair has a sum of -2

Find the sum of 10 pairs:

1 pair = -2

10 paris = (-2) x 10 = -20

Answer: The sum of 20 terms is -20

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Answer 2

-20

Its because there are 10 even and 10 odd places in series

on 10 odd places there are summation of a series that's starting term is 2 and common difference is 4

and on 10 even places there is a series whose first term is 4 amd its common difference is also 4 , but with negative sign

by applying summation formula we will find the answer (-20)