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Thread: work out missing angle?

  1. Dec 16th 2010, 06:05 AM #46
    bjhopper
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    Hiandyboy,
    Suggestions
    1 Construct the given sided triangle. The x angle will be obtuse. By using th Pythagorean T solve for the segments on the 18 base created by the altitude on it
    2 use simple trig to find the two acute angles which added will be the angle x


    bjh
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  2. Dec 16th 2010, 07:33 AM #47
    andyboy179
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    my calculator is in degrees mode.
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  3. Dec 16th 2010, 07:37 AM #48
    andyboy179
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    would this work?

    18^2= 10^2+11^2-2x10x11xcos?

    324=100+121-220cos?

    103=-220cos?

    103/-220= -0.47

    cos?=-0.47

    ?=inverse cos(-0.47)= 118.03??
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  4. Dec 16th 2010, 07:45 AM #49
    Ackbeet
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    Yep that works. Just tack on the units of degrees to your final answer, and you're done.
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  5. Dec 16th 2010, 07:46 AM #50
    andyboy179
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    thanks alot!!! i hope we will do some more of these in calss, if not i will ask for some extra homework on them!
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  6. Dec 16th 2010, 07:47 AM #51
    Ackbeet
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    You're welcome. Have a good one!
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  7. Dec 16th 2010, 12:59 PM #52
    bjhopper
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    Hi again andyboy,
    What course are you taking? I assume its Trig or Advanced Math. You were having a lot of trouble so I explained a method that does not need the cosine rule for a 3 sided triangle. This method showed x= 117.9. It was a long way to Tipperary but you got there. The same result is obtained when you use -.468 for the value of cos x - 103/220



    bjh
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  8. Dec 17th 2010, 04:32 AM #53
    andyboy179
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    i am doing my GCSEs in maths
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« Using algebra, To solve Triangles | Missing angles »

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