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Math Help - is this right ?

  1. #1
    Junior Member
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    is this right ?

    i wonder if this is right

    4 sin^2(x) + 8 cos(x) = 7

    1 = cosē(x)+sinēx

    sinē(x) = 1-cosē(x)

    replace sinē(x) with 1-cosē(x)

    -4cosē(x)+8cos(x)+4 = 7

    replace [cos(x)=t] and extender with-1

    4tē-8t-4 = -7 <--> t1= 1/2 t2=3/2

    cos(x1)=1/2
    cos(x2)=3/2

    then you get the first x but the other ?
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  2. #2
    Senior Member
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    cos(x2) = 3/2

    Is not possible for real values of x2, so this does not give any solutions.
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  3. #3
    Junior Member
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    but the solution is right ?
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  4. #4
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    Quote Originally Posted by paulaa View Post
    but the solution is right ?
    Looks like it.

    Solutions are all x s.t. cos(x) = 1/2.

    Careful though, since there is an infinite family of such values x.
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