Question

Which term of AP: 121,117,113,....,is it's first negative term?

Answer 1

a = 121

d = -4

let a_n= 0

then

a_n = a + (n-1)d

=> 0 = 121 + (n-1)(-4)

=> 0 = 121 - 4n + 4

=> 4n = 125

=> n = 125/4

=> n = 31.25

as n must be natural number then n= 32

32^nd term is First negative number.

a₃₂ = 121 + (31)-4

= 121 - 124 = -3