` 34 +32 +30 +...+10` योगफल को ज्ञात कीजिए:

Explanation

` 34 +32 +30 +...+10`
यहाँ `" " a=34 ,d =32 -34 =30-32=-2`
माना ` " " a_n =10 rArr a+ (n-1) d=10`
` rArr " " 34 + (n-1)(-2) =10 `
` " " (n-1) (-2) =10-34`
` rArr " " (n-1) (-2) =-24`
`rArr " " n-1 =12 rArr " " n=12 +1 =13`
सूत्र ` S_n =(n)/(2)[2a +(n-1) d]` से
` " " S_13=(13)/(2) [2xx 34 +(13-1) (-2) ]`
` " " =(13)/(2) (68-24)`
` " " =(13)/(2) xx44=286`