SOLUTION: If the 6th term of an AP is -10 and 10th term is -26. Determine the 15th term of an AP.

Algebra ->  Sequences-and-series -> SOLUTION: If the 6th term of an AP is -10 and 10th term is -26. Determine the 15th term of an AP.      Log On


   

Question 1108437: If the 6th term of an AP is -10 and 10th term is -26. Determine the 15th term of an AP.
Found 2 solutions by josgarithmetic, TeachMath:
Answer by josgarithmetic(39618) About Me  (Show Source):
You can put this solution on YOUR website!
Sixth term and tenth term are 4 differences apart.

-10%2B4%28d%29=-26
4d=-26%2B10
4d=-16
d=-4

General term, A-%28n-1%29%2A4, although you do not really need to find this nor A, the first term.
A-4%28n-1%29
-
A-4%284-1%29=-10-----mistake
cross%28A-12=-10%29
cross%28A=12-10%29
cross%28A=2%29
-
General Term, cross%282-4%28n-1%29%29


Fifteenth Term?
n=15
-
cross%282-4%2814%29%29
cross%282-56%29
highlight%28cross%28-54%29%29

-

Should be, starting from n=10,
to n=15,
FOUR common differences;
-26-4-4-4-4-4
-26-20
highlight_green%28-46%29

Answer by TeachMath(96) About Me  (Show Source):
You can put this solution on YOUR website!
correct answer: 15th term = - 46.
- 54 is WRONG!