Question

which of the AP 121,117,113,......is its 1st negative number

Answer 1

Hey mate,

ATQ

a=121.         d=-4

We know,

For a(n) be negative

a(n)<0

a+(n-1)d <0

121+(n-1)*(4)<0

So,

For ans to be negative

(n-1)(-4)>121

4n >(125)

n >125/4

n >31.25

n=32

Therefore the 31st term is the negative term

- Verification

a(n)=a+(n-1)d
a(n)=121+(32-1)-4
a(n)=121+31*-4
a(n)=121-124
a (n)=-3

hope this helps you out!

Answer 2

here a=121 d=a2-a1,117-121=-4