Question

A.P : 9 17 25 कितने पद लिए जाए ताकि उनका योग 636 हो

Answer 1

Step-by-step explanation:

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

636 = n/2 { 18 + (n-1)8}

1272 = n { 18 + 8n - 8 }

1272 = n ( 8n + 10 )

1272 = 2n ( 4n + 5 )

636 = n ( 4n + 5 )

4n² + 5n - 636 = 0

n = -5 + √25-16(-636) / 8

n = -5 + √25+10176 / 8

n = -5 + √10201 / 8

n = -5 + 101 / 8

n = -5 + 101 / 8 , -5-101 / 8

n = 12 , -106/8 ( value of n can't -ve or integer)

So ,n = 12

means, Sum of 12 terms of this A.P. is 636 .