Question

Find the sum of AP: -26,- 24,- 22 ........ 36 terms.​

Answer 1

The given A.P is - 26, - 24, - 22,..... till 36 terms.

→ Sum of nth terms

= n/2 [2a + (n - 1)d]

• Here, nth term = 36
• a (First Term) = - 26
• d (Common difference) = 2

→ Sum of 36 terms

= 36/2 × [2(- 26) + (36 - 1)2]

= 18[- 52 + 35(2)]

= 18[- 52 + 70]

= 18 × 18

= 324

Sum of 36 terms is 324.

Answer 2

Tn= 36

a+(n-1)d= 36

-26+(n-1)2= 36

(n-1)2= 36+26

n-1= 62/2

n= 31+1

n= 32

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

=32/2(2(-26)+(31)2)

= 16(-52+62)

= 16*10

=160