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  1. #1
    TH1
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    Trigonometry Help

    I need help for gr 10 trigonometry since I havent done it for along time and kind of forgot what to do

    A tall building casts a shadow that is 9.2m long. At the same time a 1.8m person casts a shadow that is 0.4m long. How tall is the building? Find your answer to one decimal place.
    I thinks its 9.2/x = 0.4/1.8 and you would cross multiply to get 9.2 x 1.8=16.56/0.4 to get 41.4.

    A ramp is designed so that is rises 20cm vertically for every 1 minute horizontally. What is the vertical height of the ramp if it has a horizontal length of 4.2m?


    A tree in your yard casts a shadow that is 4.5m long. Your 1.5m tall sister casts a 1m long shadow. How tall is the tree?
    4.5 x 1.5 =6.75 6.75 /1=6.75

    A 7.6m tall telephone casts a 6.1m shadow. The nearby school casts a 15.8m shadow. How tall is the school to 2 decimal places?
    6.1 x 15.8 = 96.38 96.38/7.6=12.68

    A model of the CN tower casts a shadow that is 0.9m tall and casts a shadow that is 0.2m long.If the real CN tower casts a 123.3m shadow find the height of the tower to the nearest meter
    0.9 x 123.3 = 110.97 110.97/.2 = 554.85

    A conical coffee cup is 20cm tall and has a diameter of 8cm. A new cup is designed that is 4cm shorter. What will be the new cups diameter. Find your answer to one decimal place
    I had no idea what to do for this one

    A tree has a shadow that is 12m long. If you are 1.8m tall and cast a shadow of 1.2m, how tall is the tree.

    12 x 1.2= 14.4 14.4/1.8 = 8
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  2. #2
    Forum Admin topsquark's Avatar
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    Quote Originally Posted by TH1 View Post
    A tall building casts a shadow that is 9.2m long. At the same time a 1.8m person casts a shadow that is 0.4m long. How tall is the building? Find your answer to one decimal place.
    I thinks its 9.2/x = 0.4/1.8 and you would cross multiply to get 9.2 x 1.8=16.56/0.4 to get 41.4.
    What is "9.2 x 1.8=16.56/0.4"? How about
    9.2 \cdot 1.8 = 0.4x

    x = \frac{9.2 \cdot 1.8}{0.4} = 41.4
    (This is not the same thing as what you wrote. Ask anyone that grades papers.)

    Otherwise what you wrote is correct.

    Quote Originally Posted by TH1 View Post
    A ramp is designed so that is rises 20cm vertically for every 1 minute horizontally. What is the vertical height of the ramp if it has a horizontal length of 4.2m?
    "rises 20cm vertically for every 1 minute horizontally"
    What?

    Quote Originally Posted by TH1 View Post
    A tree in your yard casts a shadow that is 4.5m long. Your 1.5m tall sister casts a 1m long shadow. How tall is the tree?
    4.5 x 1.5 =6.75 6.75 /1=6.75
    Same comment as the first problem.

    Quote Originally Posted by TH1 View Post
    A 7.6m tall telephone casts a 6.1m shadow. The nearby school casts a 15.8m shadow. How tall is the school to 2 decimal places?
    6.1 x 15.8 = 96.38 96.38/7.6=12.68

    A model of the CN tower casts a shadow that is 0.9m tall and casts a shadow that is 0.2m long.If the real CN tower casts a 123.3m shadow find the height of the tower to the nearest meter
    0.9 x 123.3 = 110.97 110.97/.2 = 554.85
    Yup.

    Quote Originally Posted by TH1 View Post
    A conical coffee cup is 20cm tall and has a diameter of 8cm. A new cup is designed that is 4cm shorter. What will be the new cups diameter. Find your answer to one decimal place
    I had no idea what to do for this one
    \frac{8~cm}{20~cm} = \frac{x}{16~cm}

    Quote Originally Posted by TH1 View Post
    A tree has a shadow that is 12m long. If you are 1.8m tall and cast a shadow of 1.2m, how tall is the tree.

    12 x 1.2= 14.4 14.4/1.8 = 8
    Yup.

    -Dan
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  3. #3
    TH1
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    For my work I wasnt sure how to type it in but I show my work the way you did it. For the question about the ramp it rises 20cm vertically for every 1 meter horizontally
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  4. #4
    Forum Admin topsquark's Avatar
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    Quote Originally Posted by TH1 View Post
    For my work I wasnt sure how to type it in but I show my work the way you did it. For the question about the ramp it rises 20cm vertically for every 1 meter horizontally
    So
    \frac{20~cm}{1~m} = \frac{x}{4.2~m}

    -Dan
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  5. #5
    TH1
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    Thanks for the help i forgot to post 2 questions so here they are

    A park desinger placed survey posts as shown in the diagram below. Measurements were made as indicated. How wide is the pond? Find your answer to 1 decimal place. The first number is 18 the bottom one is 5 and the horizontal one is 30

    I thinks its 5 x 30=150 150/18=8.3




    Explain why similar triangles cant be used to measure the height of the tree in the diagram.



    The first triangle is 8m and 18degrees the second smaller triangle is 2m and 24degress. I dont know why the triangles cant be used.
    Last edited by TH1; July 31st 2007 at 03:33 PM.
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