Arithmetic sequence

Determine the sum of the first 12 terms of an AP (arithmetic sequence) if a4 is equal to 7 and a8 is equal to minus 1.

Correct answer:

s =  24

Step-by-step explanation:

n=12 a4=7 a8=1  a8 = a4 + (84) d  d=84a8a4=84(1)7=2  a4 = a1 + 3d  a1=a43 d=73 (2)=13  a12=a1+(n1) d=13+(121) (2)=9  s=n 2a1+a12=12 213+(9)=24

Did you find an error or inaccuracy? Feel free to write us. Thank you!

You need to know the following knowledge to solve this word math problem:

Related math problems and questions: