Question

find the first negative term of the Arithmetic progression 129,120,111​

Answer 1

Answer:

-6

..................

Answer 2

Answer:

$ap = 129 \: \: 120 \: \: 111.......$

a = 129

d (common difference) = 120-120 = -9

First -ve term = Term after place of 0

So , place of 0 =

According to the formula:

an = a+ (n-1)d

0 = 129 +(n-1)-9

0 = 129 -9n +9

9n = 138

n = 138/9

n = 15.33

Place of 0 = 15.33

So , place of first -ve term = 16th place

a = 129 + ( 16 -1)-9

= 129 +(-135)

= 129-135 = -6

1st -ve term is -6