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.
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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
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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