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Math Help - Does this looks ok!

  1. #1
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    Does this looks ok!

    Given:

    SinA= -4/5
    CosA= 3/5

    CosA= radical8/3
    CosB= -1/3

    So the question is: cos(A-B) =cosA*cosB+sinA*sin(B)

    (3/5)(-1/3)+(-4/5)(radical8/3)
    -3/15+(-4radical8/15)= -3-4radical8/15

    is this right!
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  2. #2
    Forum Admin topsquark's Avatar
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    Re: Does this looks ok!

    Quote Originally Posted by TrimHonduras View Post
    Given:

    SinA= -4/5
    CosA= 3/5

    CosA= radical8/3
    CosB= -1/3

    So the question is: cos(A-B) =cosA*cosB+sinA*sin(B)

    (3/5)(-1/3)+(-4/5)(radical8/3)
    -3/15+(-4radical8/15)= -3-4radical8/15

    is this right!
    Aside from the SinB typo and needing parenthesis this is correct.

    The correct answer is (-3 - 4radical8)/15.

    Using LaTeX this is \frac{-3 - 4 \sqrt{8}}{15}. (See our LaTeX Help Forum!)

    You can also simplify a bit. What is \sqrt{8} in terms of \sqrt{2}?

    -Dan
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