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Math Help - isosceles triangles help!

  1. #1
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    isosceles triangles help!

    I am given an isosceles triangle ABC where the measure of angle b is equal to the measure of angle c. The apex angle is 120 degrees and AB is equal to 10. Find height.

    In a similar one the apex angle is 150 with a height of 16. I need to find AB.

    I tried using the textbook and class notes but I still do not understand these problems.

    Any help is greatly appreciated!
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  2. #2
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    Quote Originally Posted by Wlu2 View Post
    I am given an isosceles triangle ABC where the measure of angle b is equal to the measure of angle c. The apex angle is 120 degrees and AB is equal to 10. Find height.

    In a similar one the apex angle is 150 with a height of 16. I need to find AB.

    I tried using the textbook and class notes but I still do not understand these problems.

    Any help is greatly appreciated!
    HI

    YOu can use the cosine rule to get BC . THen draw a perpendicular line from A to BC where this line would divide the line BC into 2 equal parts .

    BC=10 , half of BC = ... , use the phythagoras to get the height .
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  3. #3
    Grand Panjandrum
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    Quote Originally Posted by Wlu2 View Post
    I am given an isosceles triangle ABC where the measure of angle b is equal to the measure of angle c. The apex angle is 120 degrees and AB is equal to 10. Find height.

    In a similar one the apex angle is 150 with a height of 16. I need to find AB.

    I tried using the textbook and class notes but I still do not understand these problems.

    Any help is greatly appreciated!
    Draw a picture (with the bisector of the apex angle) and write in the angles for the triangle, you will note that for the first you have a number of 30,60,90 triangles and from that you should be able to write down the solutions.

    The second is more fiddly as you have 15,75,90 triangles but essentially the same

    CB
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