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Math Help - Help with angles?

  1. #1
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    Help with angles?

    A river runs parallel to a block of flats. The roof of this block is 20m above the water level of the river. From a point R on the roof, looking directly across the river, the angle of depression of the nearer bank N is 43 degrees and the angle of depression of the farther bank F is 23 degrees. The bottom of the block of flats may be regarded as a point B.

    a) Draw a diagram to display this information, showing clearly the points R, B, F and N and the angles of depression.

    b)Calculate the width of the river, FN, correct to 3 significant figures

    c) Calculate the distance from the roof to the near side of the river, RN, correct to the nearest whole number.

    Im really stuck with how i draw the diagram? And then the method of how to work out the other questions. If anyone can help it'd be much appreciated.

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  2. #2
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    Re: Help with angles?

    sketch ...
    Attached Thumbnails Attached Thumbnails Help with angles?-rivertrig.png  
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  3. #3
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    Re: Help with angles?

    could you please post the method of working out the other questions b and c
    thank you
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  4. #4
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    Re: Help with angles?

    let |BN| = x , |NF| = w

    \tan(43^\circ) = \frac{20}{x}

    \tan(23^\circ) = \frac{20}{x+w}

    solve the system for x and w , then you can answer (c) using Pythagoras.
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