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# Geometric Progression / Arithmetic Q watch

1. Currently stuck on this question. What I do is I first write down the first / 2nd / 4th terms of the geometric progression which would be :

a+ar+ar^3

Then the first 3 terms of the arithmetic one would be:
a+a+d+a+2d

Now I'm confused on the next step, do I equate them now ? Don't really know what I have to show.
2. (Original post by WildBerry)

a+ar+ar^3
There's no need to sum them.

Considering the AP, look at the difference between the second and the first term, and the difference between the third and the second term; see if you can generate an equation out of that.
3. Okay so the Gp terms will be :
a , ar , ar^3

The differences of the AP terms are :
(a+d) - (a) = d
(a+2d) - (a+d) = d ?

Not really sure how to go about finding the equation to link them together as I have a D term in the AP and not in the Gp
4. (Original post by WildBerry)
Okay so the Gp terms will be :
a , ar , ar^3

The differences of the AP terms are :
(a+d) - (a) = d
(a+2d) - (a+d) = d ?

Not really sure how to go about finding the equation to link them together as I have a D term in the AP and not in the Gp
The clue is that the difference of the two terms is the same, but you know what those terms are when expressed as part of the GP,

E.g. the second minus the first term is "ar - a"

....

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