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posted by Riana Tuesday, January 1, 2013 at 6:27pm.
t11=19 and t17=61.then what will be S12? arithmetic series question
a+10d = 19 a+16d = 61 subtract them 6d = 42 d = 7 a + 70 = 19 a = -51 sum(12) = (12/2)(-102 + 11(7) ) = -150
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