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Math Help - Triangle height?!

  1. #1
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    Post Triangle height?!

    i need urgent help!!!

    i need a formula for this question...

    In this diagram, the area of a pentagon is 800 square centimeters.


    What is the area of the green part, in square centimeters? Please round up to the nearest whole number, and submit only the answer.






    i found the side length of the pentagon to be
    21.56cm


    please help me find the height of the green triangle?!
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  2. #2
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    Exclamation hmmm

    i understand that the formula for the area of a triangle is (b*h)/2

    if got the base, i just dont know how to find the height... can anyone help?

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  3. #3
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    Hello, himachuu!

    You've done an admirable part of work already . . .



    In this diagram, the area of a pentagon is 800 square centimeters.


    What is the area of the green triangle in cm² ?
    Round up to the nearest whole number.

    i found the side length of the pentagon to be 21.56cm. . . . . Good!

    An interior angle of a regular pentagon is 108°.
    Hence, a base angle of the green isosceles triangle is 72°.

    The height of the triangle is: . h \:=\:\frac{21.56}{2}\tan72^o \:\approx\:66.35 cm.

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  4. #4
    Member Henderson's Avatar
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    Hopefully it will help if I remind you that each interior angle in a pentagon is 108 degrees, so each exterior angle is 72...

    See if you can find your height using \tan(72).
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  5. #5
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    Quote Originally Posted by Soroban View Post
    Hello, himachuu!

    You've done an admirable part of work already . . .



    An interior angle of a regular pentagon is 108°.
    Hence, a base angle of the green isosceles triangle is 72°.

    The height of the triangle is: . h \:=\:\frac{21.56}{2}\tan72^o \:\approx\:66.35 cm.


    so basically all i need to do is go...

    (66.35 * b)/2?


    thank you sooo much ^^
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  6. #6
    Member Henderson's Avatar
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    Soroban!!! That's twice tonight!!!
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