given A3 is equal to 15 S10 is equal to 125 find d and A10
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Sequences and Series
Arithmetic Progres
MATHS
In an AP, given a
3
=15,S
10
=125, find d and a
10
.
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ANSWER
a
3
=15,s
10
=125
a
3
=a+(3−1)d
15=a+2d
a=15−2d
s
10
=
2
10
[2a+(10−1)d]
125=5[2a+9d]
25=2a+9d
25=2(15−2d)+9d
25=30−4d+9d
5d=−5
d=−1
a=15−2×(−1)
a=17
a
10
=a+(10−1)(−1)
a
10
=17−9
a
10
=26
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