Find the sum of 12th term of the following AP series 7,11 and 15.
2 answers:
Answer:the sum of the 12th term of the AP is 348
Step-by-step explanation:
7,11,15
Common difference=d=11-7
d=4
First term=7
Using the formula
Sn=n/2 x (2a+d x (n-1))
S12=12/2 x (2x7+4x(12-1))
S12=6 x (14+4x11)
S12=6 x (14+44)
S12=6 x 58
S12=348
It is adding 4 each time.
Just calculate the first 12 terms and add them up.
Term 1 = 7 + 4*0 = 7
Term 2 = 7 + 4*1 = 11
Term 3 = 7 + 4*2 = 15
Term 4 = 7 + 4*3 = 19
Term 5 = 7 + 4*4 = 23
Term 6 = 7 + 4*5 = 27
Term 7 = 7 + 4*6 = 31
Term 8 = 7 + 4*7 = 35
Term 9 = 7 + 4*8 = 39
Term 10 = 7 + 4*9 = 43
Term 11 = 7 + 4*10 = 47
Term 12 = 7 + 4*11 = 51
Sum of first 12 terms = 348
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