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# C1 question help Watch

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1. Translating from welsh so bear with me:

"The Coordinates of A, B, and C are (6, -3), (-10,9) and (12,5), respectively. Find out the lengths of the lines AB, BC, CA. Prove it is a right angle triangle"

I've found out the lengths (AB: 20, BC: 10√5, CA: 10), but i don't know how to prove it's a right angle triangle.
2. (Original post by jackman420)
Translating from welsh so bear with me:

"The Coordinates of A, B, and C are (6, -3), (-10,9) and (12,5), respectively. Find out the lengths of the lines AB, BC, CA. Prove it is a right angle triangle"

I've found out the lengths (AB: 20, BC: 10√5, CA: 10), but i don't know how to prove it's a right angle triangle.
Pythagoras

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3. Work out the gradient of the three lines. If there is a right angle, there must be two lines that are perpendicular to each other meaning:

So if there was a line that had gradient 3/4 and another that had gradient -4/3, then those two lines are perpendicular so there would be a right angle.

What you did there was just the first step.

Btw, I'm also doing C1, so I'm not exactly sure I'm getting this correct.
4. Got 500=500 using pythagoras. thanks mate
5. (Original post by Baaah)
Work out the gradient of the three lines. If there is a right angle, there must be two lines that are perpendicular to each other meaning:

So if there was a line that had gradient 3/4 and another that had gradient -4/3, then those two lines are perpendicular so there would be a right angle.

What you did there was just the first step.

Btw, I'm also doing C1, so I'm not exactly sure I'm getting this correct.
This is also a nice method that I will keep in mind. Thanks
6. (Original post by jackman420)
This is also a nice method that I will keep in mind. Thanks
Good idea, it will become important when you look at coordinate geometry of lines intersecting circles (in C2 if you do Edexcel)

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