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posted by Writeacher

the 8th term of an A.P is twice the 5th term
> a + 7d = 2(a+4d)
a+7d = 2a + 8d
a = d
12th term = a + 11d
= d + 11d
= 10d
e.g. let d = 4, then a = 4
term(8) = 4 + 7(4) = 24
term(5) = 4 + 4(4) = 12
so term 8 is twice term 5
term 12 = 4+11(4) = 40 which is 10d or 10(4)
As you can see there is so unique answer to your problem, just let d equal anything you want, as long as "a" is its opposite, it will work
posted by Reiny
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