Question
In arithmetic sequence tn find:
t5 , if t7=−20 and S8 = −100
t5 =
t5 , if t7=−20 and S8 = −100
t5 =
Answers
oobleck
the common difference is just t8-t7 = -80
Now t5 = t7 - 2d = -20 - 2(-80) = 140
Now t5 = t7 - 2d = -20 - 2(-80) = 140
plshelp
It's sum of 8 not T8
oobleck
oops. well, just use the right formulas, which I'm sure you know
a+6d = -20
8/2 (2a+7d) = -100
solve for a and d, and then t5 = a+4d
a+6d = -20
8/2 (2a+7d) = -100
solve for a and d, and then t5 = a+4d