a3=15,S10=125 find a and a10
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Step-by-step explanation:
a3=15
a+2d=15
multiple by 2 we get,
2a+4d=30(eqn 1)
s10=125
n÷2(2a +(n-1)d)=125
10÷2(2a+(10-1)d)=125
5(2a+9d)=125
2a+9d=125÷5
2a+9d=25(eqn 2)
on solving 1 and 2
2a + 4d =30
2a + 9d =25
- - -
-5d =5
d = -1
put in eqn 1
2a + 4d =30
2a +4(-1)=30
2a -4 =30
2a=30+4
2a=34
a=34÷2
a=17
a10 =a+9d
a10=17+9( -1)
a10=17-9
a10=8
a=17
a10=8
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