Question

-. The sum of the series a-(a+d)+(a +2d)-(a +3d) +... up to 2n+1 terms is
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Answer 1

Answer:

(2n+1)×(a+n)d

Step-by-step explanation:

a1 = a

N = 2n + 1

d=d

Sn = N/2(2a1 +(N-1)d) = (2n+1)/2 × (2a + 2n+1-1)d = (2n+1)/2 × 2(a+n)d = (2n+1)×(a+n)d

hope this answer helps you .

Answer 2

Answer:

- { a + d(n+1)}

Step-by-step explanation:

The sum of the series a-(a+d)+(a +2d)-(a +3d) +... up to 2n+1 terms = S

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