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Math Help - Sum and diffrence Formulas

  1. #1
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    Sum and diffrence Formulas

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  2. #2
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    k well i got 11, but still stuck on the other 2.

    for 10 sin(A+B) i got -84/85 but it says im wrong!!! am i? im sure its -84/85. but i did get the cos which was 77/85..
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  3. #3
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    I'd like to help but can't see your questions???
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  4. #4
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    how about now?


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  5. #5
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    woot i got them all... just 1 prob left which i dont know...


    Find the exact value of the following.
    sin(165) =


    so its somthing to deal with breaking it up into 2

    so it would be like 90-30-45 adn then the 90 cancels out and you find the sin of 30 and 45 and u liek mutiply or somthing i forget. can someone help me on this. and no u cant put this in the calculator..
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  6. #6
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    If I understand correctly then you would be looking for values on your trig circle (pi/2, pi) and then finding the sin values (sqrt2/2 for example.)

    step 1) find what 30 and 40 degrees are equal to on the trig circle

    step 2) get both sin values

    step 3) multiply them both

    I believe this is the correct path to follow
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  7. #7
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    Not too sure abut the previous reply????
    Have a go at this:
    Sin 165 = sin (90+75) = cos 75 (from the unit circle).
    Then cos 75 = cos(45+30) and use you cos(a+b) rule.
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