1.

Which term of the AP: 21, 18, 15, is 0?

Answer» series of AP is `21,18, 15 .... 0`
`a= 21`
`d= 18- 21= -3`
`T_n = a + (n-1)d = 21 + (n-1)(-3)`
`21-3n +3`
`= 24 - 3n`
`T_n=0`
`24- 3n = 0`
`24 = 3n`
`n= 8`
Answer


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