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1. https://cdn.discordapp.com/attachmen...60/unknown.png
https://cdn.discordapp.com/attachmen...01/unknown.png

I tried to do a substitution with 2 equations but i got a really horrible quadratic with massive numbers and of course it didn't factorise but when i came to use the formula on it, it turned out the formula didn't work anyway.

How am i supposed to approach this question? The second part finding K and r
2. (Original post by will'o'wisp2)
https://cdn.discordapp.com/attachmen...60/unknown.png
https://cdn.discordapp.com/attachmen...01/unknown.png

I tried to do a substitution with 2 equations but i got a really horrible quadratic with massive numbers and of course it didn't factorise but when i came to use the formula on it, it turned out the formula didn't work anyway.

How am i supposed to approach this question? The second part finding K and r
Given the answers are to 1 dec.pl, I wouldn't expect the quadratic to factorise.

I think it's just a case of ploughing through with the formula - which did work when I tried. I wasn't being careful, and there may be an error. I ended up with

Arithmetic slip somewhere?
3. (Original post by ghostwalker)
Given the answers are to 1 dec.pl, I wouldn't expect the quadratic to factorise.

I think it's just a case of ploughing through with the formula - which did work when I tried. I wasn't being careful, and there may be an error. I ended up with

Arithmetic slip somewhere?
hmm, let me try again i'll report back asap
4. (Original post by ghostwalker)
Given the answers are to 1 dec.pl, I wouldn't expect the quadratic to factorise.

I think it's just a case of ploughing through with the formula - which did work when I tried. I wasn't being careful, and there may be an error. I ended up with

Arithmetic slip somewhere?
man i get

but nvm it's ok forget this one for now, i'll let it rest
5. (Original post by will'o'wisp2)
man i get

but nvm it's ok forget this one for now, i'll let it rest
Just worked out a different route, avoiding the quadratic.

In order to avoid the subscripts, I'll use T for P_{n+1} and S for P_n

Our formula then becomes:

Which after multplying up, and grouping the K terms together, gives:

Plug in the two sets of values for S and T to get two equations, in K and r.

Then divide one equation by the other, eliminating K and the 1-r, and after multiplying up, you're left with a linear equation in r.

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