finding the nth term
Algebra
Level
pending
The 12th term of an arithmetic progression is -16 and the 6 term is -4.Find the 8th term.
The answer is -8.
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Without solving for a 1 , we can use the formula: a n = a m + ( n − m ) d . We have
a n = a m + ( n − m ) d
− 1 6 = − 4 + ( 1 2 − 6 ) d
− 1 2 = 6 d
d = − 2
Use again the formula to solve for a 8 . We have
a 8 = a 6 + ( 8 − 6 ) d = − 4 + ( 2 ) ( − 2 ) = − 8