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# Edexcel as maths proofs watch

1. What proofs do we need to know?

Thank you
2. prove that something can be shown as what they show
3. (Original post by Dinaa)
What proofs do we need to know?

Thank you
You are expected to know the proofs for the sums of arithmetic and geometric series.
4. quadratic formula, sum of arithmetic series - C1
log rules, sum of geometric series , and sine and cosine rules i think C2

( the only ones mentioned on the spec are the arithmetic & geometric series ones,the others are in the books so i assume we should know them)
5. (Original post by Dinaa)
What proofs do we need to know?

Thank you
Any of the trigonometric identities in C3/C4.
6. Thank you dolls
7. Proof that the shortest distance between two points is always a straight line

Proof of irrationality of Pi (3.14159...)

Just kidding, you don't specifically need to know these, but can you do these basic proofs? Most math teachers not from really good schools would probably struggle on these.
8. apparently you need to know the proof for the quadratic formula
9. (Original post by BBeyond)
apparently you need to know the proof for the quadratic formula
that one you could probably just figure out on the spot
10. (Original post by CancerousProblem)
that one you could probably just figure out on the spot
well yeah it's just completing the square
11. (Original post by CancerousProblem)
Proof that the shortest distance between two points is always a straight line

Proof of irrationality of Pi (3.14159...)

Just kidding, you don't specifically need to know these, but can you do these basic proofs? Most math teachers not from really good schools would probably struggle on these.
You think the proof of irrationality of pi is basic?

how old are you..like 12?
12. (Original post by newblood)
You think the proof of irrationality of pi is basic?

how old are you..like 12?
actually nevermind, I meant e.
wrong number

Proof of Pi's irrationality is not basic. Honestly, I think teachers ought to stop telling studnets Pi is irrational though, and stick to square roots as their main example.
13. (Original post by CancerousProblem)
Proof that the shortest distance between two points is always a straight line
I'm under the impression that this is decidedly non-trivial, unless you have the machinery of the Euler-Lagrange equations - if you have an easy proof I'd like to see it.
14. (Original post by Dinaa)
What proofs do we need to know?

Thank you
You will barely be asked prove something out of nowhere, except for a given quadratic equation or inequalities, maybe prove that 3 consecutive points make a right angle triangle.

I would recommend doing an AQA past paper as there are a lot of harder questions to do with those type of proofs I have mentioned (particularly the 3 most recent ones).
15. (Original post by Smaug123)
I'm under the impression that this is decidedly non-trivial, unless you have the machinery of the Euler-Lagrange equations - if you have an easy proof I'd like to see it.
Proof:
Assume the opposite is true
Then the line must be 'bent' or have an angle on at least one point. (A curved line is just an infinite number of angles.)
By the cosine rule the shortest distance across the bend is when the bend is at 180 degrees
ie a straight lien
therefore for any curve that has a bend or vertice not of 180 degrees there is always a curve that exists such that that it is shorter but still reaches the two points
done
16. (Original post by CancerousProblem)
Proof:
Assume the opposite is true
Then the line must be 'bent' or have an angle on at least one point. (A curved line is just an infinite number of angles.)
By the cosine rule the shortest distance across the bend is when the bend is at 180 degrees
ie a straight lien
therefore for any curve that has a bend or vertice not of 180 degrees there is always a curve that exists such that that it is shorter but still reaches the two points
done
I don't like your explanation for curves. As an intuition, fine, but curves can be really weird objects and calling it "just an infinite number of angles" is just asking for trouble. Additionally, I think you're assuming certain differentiability properties on the curve which might not necessarily be present.
17. Im intrigued, what is this supposed to mean?

(Original post by kkboyk)
prove that 3 consecutive points make a right angle triangle.
18. (Original post by newblood)
Im intrigued, what is this supposed to mean?
You are given 3 points let's say they are A, B and C. They form a right angle triangle, and using the knowledge you learn from coordinate geometry you have to prove that they form a right angle triangle.

So what you do is find the gradient of the lines joining these points, so the gradient of AB, AC and BC. They form a right angle triangle if the gradient of two of these light are perpendicular and equals -1 if you multiply them together.
19. (Original post by kkboyk)
You are given 3 points let's say they are A, B and C. They form a right angle triangle, and using the knowledge you learn from coordinate geometry you have to prove that they form a right angle triangle.

So what you do is find the gradient of the lines joining these points, so the gradient of AB, AC and BC. They form a right angle triangle if the gradient of two of these light are perpendicular and equals -1 if you multiply them together.
But you said three consecutive points form a right angle triangle. What does consecutive mean in this context?
20. (Original post by newblood)
But you said three consecutive points form a right angle triangle. What does consecutive mean in this context?
Oh sorry ignore it. I made a few errors when writing on my phone so it auto corrected an error into that.

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