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Math Help - general solutions

  1. #1
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    general solutions

    write a general solution for
    cos3x=(-sin2x)

    I changed sin to cos and then solved the equation and got the general solution of x = 2npi + (pi)/2 OR x= (4npi-pi)/10

    Can anyone tell me if this is correct or not?
    Much appreciated.

    And for this question

    y=5sin(3x-pi/4) has maximum and minimum values at?

    Well, i said it has max and min values at y=5 and -5 and then i solved the equation
    For maximum values, when y=5

    I got x = [4npi+(-1)^n(2pi) +pi]/12

    I would really really appreciate it if someone could check that for me and tell me if it's right or wrong

    THankyou =)
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  2. #2
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    Quote Originally Posted by christina View Post
    write a general solution for
    cos3x=(-sin2x)

    I changed sin to cos and then solved the equation and got the general solution of x = 2npi + (pi)/2 OR x= (4npi-pi)/10

    Can anyone tell me if this is correct or not? Mr F says: Correct.
    Much appreciated.

    And for this question

    y=5sin(3x-pi/4) has maximum and minimum values at?

    Well, i said it has max and min values at y=5 and -5 and then i solved the equation
    For maximum values, when y=5

    I got x = [4npi+(-1)^n(2pi) +pi]/12 Mr F says: Wrong. You require {\color{red} 3x - \frac{\pi}{4} = \frac{\pi}{2} + 2n \pi \Rightarrow x = ....}.

    I would really really appreciate it if someone could check that for me and tell me if it's right or wrong

    THankyou =)
    ..
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