Need a trig explanation?

I came across questions that might be asked on my Trig Final that I have no idea how to do. If you could tell me how to do these? An example problem:

Given that cos x + i sin y = sin x + i, find all correct x and y values between 0 and 2pi.

Update:

@Maurice

That response doesn't really tell me how to do these problems at all...

2 Answers

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  • Dragon
    Lv 6
    7 years ago
    Favorite Answer

    Here's what I did:

    a) Rewrite equation to put one unknown (and i) on one side to get

    cos(x) - sin(x) = i - i[sin(y)]

    b) square both sides to get

    cos^2(x) - 2(cos(x))(sin(x)) + sin^2(x) = i^2 - 2(i^2)(sin(y)) + i^2(sin^2(y))

    c) substitute 1 for cos^2 + sin^2 on the left side; and i^2 = [sqrt(-1)]^2 or -1 on the right side to get

    1 - 2(cos(x))(sin(x)) = -1 + 2(sin(y)) - 1(sin^2(y) = - (1 - sin(y))^2

    d) multiply both sides of the equation by -1 and reverse left and right sides of equation to get

    (1 - sin(y))^2 = 2(cos(x))(sin(x))

    e) take sqrt of both sides to get 1 - sin(y) = sqrt[2(cos(x))(sin(x)]

    f) subtract 1 from each side to get - sin(y) = sqrt[2(cos(x))(sin(x)] -1

    g) divide both sides by -1 to get sin(y) = 1 - sqrt[2(cos(x))(sin(x)]

    h) y = sin^-1 [1 - sqrt[2(cos(x))(sin(x)]

    i) input above equation into graphing calculator and use trace function to input x values to get desired y values or manually input x values to get corresponding y values

    Source(s): Good luck, Dragon
  • 7 years ago

    equate real and imaginary parts

    cosx = sinx; x = pi/4, pi+pi/4

    siny = 1; y =pi/2

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