Question

find the sum of last ten terms of AP 8,10,12.....,126.

Answer 1

a/c to question ,
we invert this series ,
126 , 124 , 122 ,........8

now,
first term of new AP is = 126
common difference = -2

use formula,
Sn =n/2 {2a +(n-1)d

S10=10/2{2 × 126 +(10-1)(-2)}
=5{252 -18}
=5 × 234
=1170

Answer 2

Answer:

a/c to question ,

we invert this series ,

126 , 124 , 122 ,........8

now,

first term of new AP is = 126

common difference = -2

use formula,

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

S10=10/2{2 × 126 +(10-1)(-2)}

=5{252 -18}

=5 × 234

=1170