Question

Find the number of terms of the AP -12 , -9 , -6 ......, 12. If 1 is added to each term of this AP then find the sum of all terms of the AP thus obtained.

Plzzz help me ​

Answer 1

Answer:

n=9, sum also equals to 9

Step-by-step explanation:

from the question a =-12, d= +3

an=12

but an= a+(n-1)d

12=-12+(n-1)3

24 = (n-1)3

n-1=8

n=9

so you are adding 1 to every number that means

a=-11

an=13

but d will be same

n=9

find sn

sn= (n/2)*(a+l)

sn= 9/2*(-11+13)

sn= 9/2*2

sn=9