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# FP1 matrix question

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1. So this type of question is my main problem in FP1.
In Q4c, why R=QP but not R=PQ? What is the difference between them?
2. (Original post by alesha98)

So this type of question is my main problem in FP1.
In Q4c, why R=QP but not R=PQ? What is the difference between them?
Think of it like a function. A matrix is a "function" that you feed it in a point and it gives out a point.

So QP = Q(P), that is you feed Q the "point"/"matrix" P and not the other way around, basically think of it like compositions of functions.

Is the same thing as ? Hell nah!

In the question, it says T (R) is the transform U (P) followed by V (Q).

That is, the transform T takes some point , you then put it through the function/transform "P" to get , this is the point. Now you take this new point and you put it in your new function/transform "Q" to get Q(P(x)). Just like function composition.

You then drop the brackets and remove the "x", of course, so: R = QP is P followed by Q.

Does that make sense? I can explain more if you'd like.
3. (Original post by Zacken)
Think of it like a function. A matrix is a "function" that you feed it in a point and it gives out a point.

So QP = Q(P), that is you feed Q the "point"/"matrix" P and not the other way around, basically think of it like compositions of functions.

Is the same thing as ? Hell nah!

In the question, it says T (R) is the transform U (P) followed by V (Q).

That is, the transform T takes some point , you then put it through the function/transform "P" to get , this is the point. Now you take this new point and you put it in your new function/transform "Q" to get Q(P(x)). Just like function composition.

You then drop the brackets and remove the "x", of course, so: R = QP is P followed by Q.

Does that make sense? I can explain more if you'd like.
I am so sorry, but i still dont get it
4. (Original post by alesha98)
I am so sorry, but i still dont get it
If we have the function and the function , how would you write down "f(x) composed with g(x)"?
5. (Original post by Zacken)
If we have the function and the function , how would you write down "f(x) composed with g(x)"?
hmm i dont know ... is it in C1 or C2 syllabus?
6. (Original post by alesha98)
hmm i dont know ... is it in C1 or C2 syllabus?
I don't really know how to break it down in any simpler way ('cause I'm dumb). If you want a more systematic rule, you could just go:

QP is P followed by Q.
PQ is Q followed by P.
7. (Original post by alesha98)
hmm i dont know ... is it in C1 or C2 syllabus?
The easiest way to show they're not the same is by doing the calculation of both. Do this and you should get different answers
8. (Original post by Zacken)
I don't really know how to break it down in any simpler way ('cause I'm dumb). If you want a more systematic rule, you could just go:

QP is Q followed by P.
PQ is P followed by Q.
So in this question, UV = T, so i thought it would be PQ= R, because P represents U and Q represents V. But i know i am wrong?
9. (Original post by alesha98)
So in this question, UV = T, so i thought it would be PQ= R, because P represents U and Q represents V. But i know i am wrong?
No, in this question it's U followed by V. That is, U first and then V second.

And the second one comes first, (I know it's weird, but that's how it is):

So it's VU = T.

As to why the second one comes first, well, you'll need to re-read my first post.
10. (Original post by Zacken)
No, in this question it's U followed by V. That is, U first and then V second.

And the second one comes first, (I know it's weird, but that's how it is):

So it's VU = T.

As to why the second one comes first, well, you'll need to re-read my first post.
Do you know what is this rule or topic called, so i can look it up on youtube?
11. (Original post by alesha98)
Do you know what is this rule or topic called, so i can look it up on youtube?
This video explains it really well.
12. (Original post by Zacken)
This video explains it really well.
13. (Original post by alesha98)
You're welcome.
14. (Original post by Zacken)
I don't really know how to break it down in any simpler way ('cause I'm dumb). If you want a more systematic rule, you could just go:

QP is Q followed by P.
PQ is P followed by Q.
The video is really clear , and i think QP is not Q followed by P. It should be P followed by Q
15. (Original post by alesha98)
The video is really clear , and i think QP is not Q followed by P. It should be P followed by Q
Yep, you're right. That was me in my haze of tiredness, I'll correct it now - glad the video was useful.
16. (Original post by Zacken)
Yep, you're right. That was me in my haze of tiredness, I'll correct it now - glad the video was useful.
yes thankyou for helping when u are tired, that was very helpful.
17. (Original post by alesha98)
yes thankyou for helping when u are tired, that was very helpful.
No problem.

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