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Math Help - A question, distance formula, triangle

  1. #1
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    Question A question, distance formula, triangle

    Show that (4,5,2) ,(1,7,3),and (2,4,5) are vertices of an equilaterial triangle.

    Please teach me how to solve this question. Thank you very much.
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  2. #2
    Grand Panjandrum
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    Quote Originally Posted by Jenny20 View Post
    Show that (4,5,2) ,(1,7,3),and (2,4,5) are vertices of an equilaterial triangle.

    Please teach me how to solve this question. Thank you very much.
    Compute the (square)distances between the points, if they are equal, then you have
    an equilateral triangle.

    first two:

    D^2=(4-1)^2+(5-7)^2+(2-3)^2=9+4+1=14

    first and third:

    D^2=(4-2)^2+(5-4)^2+(2-5)^2=4+1+9=14

    second and third:

    D^2=(1-2)^2+(7-4)^2+(3-5)^2=1+9+4=14

    QED

    RonL
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  3. #3
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    Hello, Jenny!

    Show that (4,5,2) ,(1,7,3),and (2,4,5) are vertices of an equilaterial triangle.

    Please teach me how to solve this question.

    You really should be able to reason this out yourself, Jenny.

    Three (non-collinear) points always form a triangle.
    What makes an equilateral triangle different from other triangles?
    . . It has three equal sides, right?

    How are you going to show that?'
    How can we possibly find the lengths of the sides?
    . . Hmmm ... how about the Distance Formula?

    Your brain should be clicking along those lines effortlessly.

    ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~

    How about another example?

    Show that (3,0), (7,3), (4,7), (0,4) are vertices of a square.


    You might make a casual graph of the points
    . . so you can see the square.

    Is your brain already working on it?

    What do you know about a square?
    . . It has four equal sides.
    And now you know how to show that, right?

    Is that all we need?
    No, four equal sides will make it a rhombus: \diamondsuit

    We need to show that the corners are right angles.
    . . (We only need to show that one of the corners is 90.
    . . If opposite sides are equal, it is already a parallelogram.)
    How do we do that?
    A right angle means that two sides are perpendicular, right?
    . . And you do know about perpendicular slopes, don't you?
    So check out the slopes of two adjacent sides.


    See? . . . All that is already in your brain.
    . . You just have to formulate a game plan.

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