The 16th term of an AP is 5 times its third term.If the 10th term is 41,then find the sum of its first fifteen terms.
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therefore the sum of its first fifteen terms of ap is 495
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Answer:
A16=5a3
a10 =41
s15,=?
a16=5(a+2d)
5a+10d
.a+9d=41......1. ( Multiply by 4)
4a+36d=164 .....2
a+15d=5a+10d=4a-5d......3
Sustract 3-2
d=4
a +36 =41
a=5
S15=n/2(20-14×4)
15/2×66
495
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