How do you find d for the arithmetic series with s17=-170 and a1=2?

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Answer 1 · 2016-08-25T02:10:44

#d = -1.5#

We use the formula #s_n = n/2(2a + (n - 1)d))# to find the sum of an arithmetic series.

In our problem, we have that #n = 17#, #s_17 = -170# and #a = 2#. We are looking for #d#.

#-170 = 17/2(2(2) + (17 - 1)d)#

#-170 = 17/2(4 + 16d)#

#-170 = 34 + 136d#

#-204 = 136d#

#d = -1.5#

Hopefully this helps!