francis

posted by vivian

if the 8th term of an A.P is twice the 5th term, find the 12th term

1. Writeacher

What subject is "francis"?

2. Reiny

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

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