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Math Help - Compound Angle Formula

  1. #1
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    Post Compound Angle Formula

    Hi everyone!

    plz help me solve this Compound Angle Formula question:

    1. Using Compound Angle Formula, prove that:

    cos(y - 180) + sin (y +
    90) = 0

    plz thxx
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  2. #2
    MHF Contributor harish21's Avatar
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    Quote Originally Posted by coolhacker View Post
    Hi everyone!

    plz help me solve this Compound Angle Formula question:

    1. Using Compound Angle Formula, prove that:

    cos(y - 180) + sin (y +
    90) = 0

    plz thxx
    cos(A-B) = (cosA \times cosB)  + (sinA \times sinB)

    sin(A+B) = (sinA \times cosB) + (cosA \times sinB)

    Now try solving your question
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  3. #3
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    Hello, coolhacker!

    We are expected to know these formulas:

    . . \cos(A-b) \;=\;\cos A\cos B + \sin A\sin B

    . . \sin(A + B) \;=\;\sin A\cos B + \cos A\sin B



    1. Using Compound Angle Formulas, prove that:

    . . . . . \cos(y - 180^o) + \sin (y + 90^o) \;=\;0

    We have: . \cos(y-180^o) \qquad\quad+ \quad\qquad\sin(y+90^o)

    . . =\;\;\overbrace{\cos y \cos180^o + \sin y \sin180^o} + \overbrace{\sin y\cos90^o + \cos y\sin90^o}

    . . =\;\;\;\cos y\,(-1) \quad+\quad \sin y\,(0) \quad+\quad \sin y\,(0) \quad+ \quad \cos y\,(1)

    . . =\qquad -\cos y \qquad + \qquad 0 \qquad + \qquad 0 \qquad + \qquad \cos y

    . . = . . . . . . . . . . . . . . . . . . 0

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  4. #4
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    thx u
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