निम्नलिखित निचे दी श्रेणी का योग ज्ञात कीजिए:
` 7+_10(1)/(2) +14 +........+84 `

Explanation

` 7+_10(1)/(2) +14 +........+84 `
यहाँ ` a=7 ,d =10 (1)/(2) -7 =14 -10 (1)/(2) =(7)/(2)`
माना `" " l =a_n =84`
`rArr " " 7+(n-1) (7)/(2) =84 " " rArr " " (n-1 )(7)/(2) =77`
` rArr " " n-1 =22 " " rArr" " n=23 `
अब, ` " " S_n =(n)/(2) (a+l) `
` rArr " "S_(23) =(23)/(2) (7+84) =(2093)/(2) `