find the sum of first 100 terms of an AP whose third and fourth terms are 10 and 16
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a + 2d = 10...............1
a + 3d = 16...............2
_________________
-d = -6
d = 6
from 1
a = 10 - 12 = -2
Sum of first 100th term
= 100/2 {2 x (-2) + 99 x 6}
= 50 ( -4 + 594 )
= 50 x 590
= 29500
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