Question

find the sum of the first 18 term of the arithmetic progression 12b,8b,4b​

Answer 1

Answer:

12b,8b,4b.

s18=?.

First term=a=12b.

Common difference=d=a2-a1=8b-12b=-4b. (Because +×-=- & largest number is important).

sn=2a+(n-1)d.

s18=2(12b)+(18-1)(-4b).

s18=24b+(17)(-4b).

s18=24b-68b.

s18=-44b.

I think this is your answer.