Question

8 times of the eight term of an arithmetic progression is equal to 12 times of the twelfth term. find its first term if the common difference is -2 .​

Answer 1

38

Explanation:

We can express the 8th term as x and the 12th term as y.

This would mean that 8x=12y

Because the common difference between terms is -2 and term 8 and term 12 are 4 terms apart, this means that the 12th term is 8 less than the 8th term, so x-8=y

Now we can use this to substitute y with x in the first equation. This would give us:

8x=12(x-8)

Which we can expand and solve:

8x=12x-96

-4x=-96

Therefore x=24

This means the 8th term is 24 and the 12th term is 16 (24-8).

To test if this is correct we can do:

8x24=12x16

Which indeed are equal, both sides multiply to 192.

Now that we have our 8th term, we can find the 1st term, which is 7 terms away, therefore we just add 14 to the 8th term 24. (7x2=14)

24+14=38.

The first term is 38.

Hope this helped!