## prove the given condition

Geometric formulae, word problems, theorems and proofs, etc.
descartes123
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### prove the given condition

Hello everybody. I am now reading a russian book on high-maths from beginning and have an exercise for you:

prove that the triangle with its summits P(-2,-1), Q(6,1) and R(3,4) is right-angle.

have a luck:)

little_dragon
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### Re: prove the given condition

prove that the triangle with its summits P(-2,-1), Q(6,1) and R(3,4) is right-angle.
find the slopes of the sides: http://www.purplemath.com/modules/slope.htm
2 lines should be perpendicluar--thats a right angel!

descartes123
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### Re: prove the given condition

you are maybe right, but I didi not mean that, i.e. I had to put this exercise in the Linear Algebra section.
The thing is that in this case we have to use a formula, describing a distance between to points.
let's say if we have two points M1(x1,y1) and M2(x2,y2). and you have to use a distance formula.

nona.m.nona
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### Re: prove the given condition

The thing is that in this case we have to use a formula, describing a distance between to points.
let's say if we have two points M1(x1,y1) and M2(x2,y2). and you have to use a distance formula.
Apply the Distance Formula to the pairs of points to find the lengths of the three sides. Then apply the Pythagorean Theorem to the lengths, to show that they represent values for a right triangle.