Question

Find the sum of last 21 terms of the AP:-
8,10,12..............126.

Answer 1

Answer:

I

Step-by-step explanation

If we have to find the sum of last 21 terms of an ap then we have to take

a= 126 d= -2

Now applying the formula

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

Putting the values..

S= 21/2 (2×126 + (21 - 1)-2)

= 21/2 (252 + 20 × (-2) )

= 21/2 (252 - 40)

= 21/2 (212)

=21× 106

=2226