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    1, obtain an expression for sin3A in terms of sin A
    2, obtain an expression for cos3A in terms of cos A
    pg 70-71 (Heinemann Pure Mathematics 2 Ex 4C)

    how do I do that?
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    (Original post by etomac)
    1, obtain an expression for sin3A in terms of sin A
    2, obtain an expression for cos3A in terms of cos A
    pg 70-71 (Heinemann Pure Mathematics 2 Ex 4C)

    how do I do that?
    use sin3A=sin(A+2A) and cos3A=cos(A+2A).Do u know what to do next?
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    yes thats what i did
    for sin
    sinAcos2A + cosAsin2A
    sinA(1-2sin^2A) + sin2AcosA
    but i dunno how to get rid of cosA and end up with a cubic function
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    (Original post by etomac)
    yes thats what i did
    for sin
    sinAcos2A + cosAsin2A
    sinA(1-2sin^2A) + sin2AcosA
    but i dunno how to get rid of cosA and end up with a cubic function
    well sin2A=2sinAcosA so cosAsin2A=2cos²AsinA
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    (Original post by IntegralAnomaly)
    well sin2A=2sinAcosA so cosAsin2A=2cos²AsinA
    ok.. i got it
 
 
 
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