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Math Help - Please Help me - Triangle Problem

  1. #1
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    Sep 2007
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    Please Help me - Triangle Problem

    Hi, I'm trying to work out what must be a very simple bit of maths but not getting very far.

    I have a triangle the angles are 90, 5 and 85

    I know length of one of the sides of the triagle is 300cm

    I need to know the lengths of the other sides.


    Your help would be greatly appreciated.
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  2. #2
    Junior Member
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    philippines
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    trigonometric formula

    hint:
    using cosine law and sine law.
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  3. #3
    MHF Contributor
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    I know length of one of the sides of the triagle is 300cm

    I need to know the lengths of the other sides


    The triangle is a right triangle because one of the 3 angles is 90 degrees.
    The side opposite the 90 degrees is called the hypotenuse.
    If by one of the sides it is meant the hypotenuse is included among the sides, then there are possibly 3 different right triangles that are solutions to your question.

    Say the general right triangle is ABC, where angle B is the 90 degrees, the angle A is the 5 degrees, and angle C is the 85 degrees.

    1) One possible triangle---when the hypotenuse, side AC, is 300 cm.

    sin(85deg) = AB/300
    AB = 300sin(85deg) = 298.86 cm.

    cos(85deg) = BC/300
    BC = 300cos(85deg) = 26.15 cmm

    ---------------
    2) Another possible triangle----if AB = 300 cm.

    sin(85deg) = 300/AC
    AC = 300 /sin(85deg) = 301.15 cm.

    tan(85deg) = 300/BC
    BC = 300 /tan(85deg) = 26.25 cm.

    ----------------------------

    3) Another possible triangle----if AC = 300 cm.

    cos(85deg) = 300/AC
    AC = 300 /cos(85deg) = 3442.11 cm.

    tan(85deg) = AB/300
    AB = 300tan(85deg) = 3429.02 cm.
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  4. #4
    Newbie
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    Sep 2007
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    Many Thanks

    My triangle is triangle 2 so the length I wanted to know is 26.25cm

    Thank you very much for your help.

    This information is to help plan a new conservatory on the back of my house.
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