` A.P. : 121,117, 113,.... ` कौन-सा पद सबसे पहला ऋणात्मक पद होगा?

Explanation

दी ` A.P. : 121,117, 113,.... `
यहाँ ` a= 121,d =117 -121 =113 -117 =-4`
माना `a_nlt 0 " " rArr " " a+ (n-1) dlt 0`
` rArr " " 121+ (n-1) (-4) lt 0 `
` rArr 121- 4n +4 lt0 " " rArr " " -4 n lt-125`
`rArr " " n gt (125)/(4) rArr" " n gt 31(1)/(4)`
` rArr " " n= 32,33,34,....`
` therefore ` प्रथम ऋणात्मक पद = 32 वां पद