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# Fp1 exam question help

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1. question 7 jan 09 fp1 aqa

i understand the theory i.e i have to prove it is linear interpolation however i can't seem to obtain the rearranged version for r - mainly the c-d part why is that needed and not just d for the similar triangles?, could someone walk it through please.

Also, on q3 am i right in thinking i have too minus the (pi divided by 2) then divide by -3?
2. Oh yeah ... horrible question
3. (Original post by TenOfThem)
Oh yeah ... horrible question
so i shouldn't feel that annoyed that i was stuck and spent a lot of time on this?
4. I seem to remember that I spent ages doing convoluted adding of stuff to make it work

Then when I was showing the class I saw a really obvious way
5. (Original post by coolstorybrother)
so i shouldn't feel that annoyed that i was stuck and spent a lot of time on this?
I spent time using the little triangles .... then in class I thought ... hang on and used this

6. (Original post by TenOfThem)
I seem to remember that I spent ages doing convoluted adding of stuff to make it work

Then when I was showing the case I saw a really obvious way
im not sure but is the really obvious way using similar triangles (r-a)/c = (b-r)/d ? could you help on q3?
7. (Original post by coolstorybrother)
im not sure but is the really obvious way using similar triangles (r-a)/c = (b-r)/d ? could you help on q3?
It is about using the correct similar triangles

see ^^^^^^
8. What is arctan(rt3)
9. (Original post by TenOfThem)
I seem to remember that I spent ages doing convoluted adding of stuff to make it work

Then when I was showing the case I saw a really obvious way
Which part of the question is difficult?
10. (Original post by raheem94)
Which part of the question is difficult?
none of it
11. (Original post by TenOfThem)
none of it
On which part did you spent ages?
I may like to have a go at it.
12. (Original post by raheem94)
On which part did you spent ages?
I may like to have a go at it.
The initial proof

As I said I used the 2 small triangles and then had to do manipulation to get the format required

But ... as my diagram shows it was very easy
13. (Original post by TenOfThem)
The initial proof

As I said I used the 2 small triangles and then had to do manipulation to get the format required

But ... as my diagram shows it was very easy
I did the 1st part in this way,

The gradient of the line(using points P(a,c) and Q(b,d) ) is,

Now form the equation of the line, using the point R(r,0),

Now sub in P(a,c), this gives,

How is this solution?
14. I did Purple ratio = Green ratio

so

so

15. (Original post by raheem94)

How is this solution?

I did similar to this before I realised the easy way I have shown above

That is what I meant when I said it took too much manipulation
16. (Original post by TenOfThem)
I did similar to this before I realised the easy way I have shown above

That is what I meant when I said it took too much manipulation
Your way is better, but it is difficult to realize that technique. Similar triangles aren't much used at A-Level, so the students will probably not spot the easy technique.

Though my way is also not very long, it only takes around a minute.
17. (Original post by raheem94)
Your way is better, but it is difficult to realize that technique. Similar triangles aren't much used at A-Level, so the students will probably not spot the easy technique.

Though my way is also not very long, it only takes around a minute.
Yeah ... from experience I just knew it should be "see-able" rather than "workable"

Once I "saw" it I was like "OMG how obvious"
18. (Original post by TenOfThem)
It is about using the correct similar triangles

see ^^^^^^
i kind of understand this... everything except why it is c-d?

(Original post by TenOfThem)
What is arctan(rt3)
umm i really dont know, should i?
19. (Original post by coolstorybrother)
i kind of understand this... everything except why it is c-d?

umm i really dont know, should i?
c-d ... yeah I had to think ... but d is already a negative number

Yes you should
20. (Original post by raheem94)
Your way is better, but it is difficult to realize that technique. Similar triangles aren't much used at A-Level, so the students will probably not spot the easy technique.

Though my way is also not very long, it only takes around a minute.
Similar triangles is widely used as a method for linear-interpolation.

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