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Solve the trigonometric equation 4\[2 x\] + 4 x = 5 for 0^ x 360^.

Mathematics

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Answer

60∘,300∘60^\circ, 300^\circ

Step-by-step solution

4 steps
  1. Use the identity sin⁡2x+cos⁡2x=1\sin^2 x + \cos^2 x = 1.

    From this identity, we can write sin⁡2x=1−cos⁡2x\sin^2 x = 1 - \cos^2 x.
    Substitute this into the given equation:

    4(1−cos⁡2x)+4cos⁡x=54(1 - \cos^2 x) + 4\cos x = 5
  2. Expand and rearrange the equation into a quadratic form.

    4−4cos⁡2x+4cos⁡x=54 - 4\cos^2 x + 4\cos x = 5

    Move all terms to one side to set the equation to zero:

    −4cos⁡2x+4cos⁡x+4−5=0-4\cos^2 x + 4\cos x + 4 - 5 = 0 −4cos⁡2x+4cos⁡x−1=0-4\cos^2 x + 4\cos x - 1 = 0

    Multiply by -1 to make the leading coefficient positive:

    4cos⁡2x−4cos⁡x+1=04\cos^2 x - 4\cos x + 1 = 0
  3. Solve the quadratic equation for cos⁡x\cos x.

    This is a perfect square trinomial, which can be factored as (2cos⁡x−1)2=0(2\cos x - 1)^2 = 0.
    Alternatively, let y=cos⁡xy = \cos x. The equation becomes 4y2−4y+1=04y^2 - 4y + 1 = 0.
    Using the quadratic formula y=−b±b2−4ac2ay = \frac{-b \pm \sqrt{b^2 - 4ac}}{2a}:

    y=−(−4)±(−4)2−4(4)(1)2(4)y = \frac{-(-4) \pm \sqrt{(-4)^2 - 4(4)(1)}}{2(4)} y=4±16−168y = \frac{4 \pm \sqrt{16 - 16}}{8} y=4±08y = \frac{4 \pm \sqrt{0}}{8} y=48y = \frac{4}{8} y=12y = \frac{1}{2}

    So, cos⁡x=12\cos x = \frac{1}{2}.

  4. Find the values of xx in the range 0∘≤x≤360∘0^\circ \le x \le 360^\circ.

    We need to find angles xx for which cos⁡x=12\cos x = \frac{1}{2}.
    The reference angle for cos⁡x=12\cos x = \frac{1}{2} is 60∘60^\circ.
    Since cos⁡x\cos x is positive, xx lies in the first and fourth quadrants.
    In the first quadrant:

    x=60∘x = 60^\circ

    In the fourth quadrant:

    x=360∘−60∘=300∘x = 360^\circ - 60^\circ = 300^\circ

    Both 60∘60^\circ and 300∘300^\circ are within the specified range 0∘≤x≤360∘0^\circ \le x \le 360^\circ.

    The solutions are 60∘,300∘60^\circ, 300^\circ.

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