Question

Find the sum of 10 terms from the last of the AP 8, 10, 12, 14,...., 126.

Answer 1

Hey friend, ☺️ here is your answer ___________________________

We have to find the sum from the last. So we write this AP in reversing order

In reversing order - - -
126,.......... 14, 12, 10, 8

From here we get the following information.
a = 126
an = 8
d = 12 - 14 = - 2
a10 = a + 9d = 126 + 9*-2 = 126 - 18 = 108

Sum of 10 terms
Sn = n/2 ( a + an)
S10 = 10/2 ( 126 + a10)
S10 = 5 (126 + 108)
S10 = 1170

Hope this helps you..

Answer 2

Hey !!!

Solution :-

a = 8
t2 = 10
d = t2 - t1 = 10 - 8 = 2
N = 10
l = 126
hence, we know that tn from last term = l - (n - 1)d

tn = 126 - (10 - 1 ) 2

tn = 126 - 18

tn = 108

•°• here question ask sum of from last term since , 126 work as first term and 108 work as last term .

then , We know sn = n/2 ( a + l )

sn = 10/2 ( 126 + 108 )

=> 5× 234

=> 1170 Answer ✔

______________________________

Hope it helps you !!!

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