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Math Help - Non-right angled trig.

  1. #1
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    Smile Non-right angled trig.

    I tried to solve this question and got the answer to be 79.8 m.
    The correct answer is apparrantly 204 m.
    I hope you can help me solve this question.

    The question:
    From point A, the angle of elevation to the top a tall building is 20 degrees. On walking 80 m towards the building the angle of elevation is now 23 degrees. How tall is the building?

    Thanks,
    Amine
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  2. #2
    Member Greengoblin's Avatar
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    You effectively have a right angled triangle split into a smaller right angled triangle, and an irregular triangle. first you can work out the angles inside the iregular triangle.

    180=20+(180-23)+A \implies A=3^{\circ}

    Next you can use the sine rule to find the hypotenuse of the smaller right angled triangle:

    \frac{80}{\sin(3)}=\frac{c}{\sin(20)}\implies c = 522.81m<br />

    then the height of the building h is given by:

    h=522.81\sin(23)=204.3m
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  3. #3
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    Quote Originally Posted by Aminekhadir View Post
    I tried to solve this question and got the answer to be 79.8 m.
    The correct answer is apparrantly 204 m.
    I hope you can help me solve this question.

    The question:
    From point A, the angle of elevation to the top a tall building is 20 degrees. On walking 80 m towards the building the angle of elevation is now 23 degrees. How tall is the building?

    Thanks,
    Amine
    Have a look here: http://www.mathhelpforum.com/math-he...879-post2.html

    second question.
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