Posted by De-Graft on Saturday, November 6, 2010 at 10:17am.
term(13) = a+12d
so a+12d = 27 (equation #1)
term(7) = 3term(2)
a+6d = 3(a+d)
a+6d = 3a + 3d
2a - 3d = 0 (equation #2)
It is easy to solve these two equations, (see if you can get a=3, d=-2)
then use your formula for the sum of 10 terms.
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