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2sin(50)cos(50) - 2cos²(50) + 3 = 0

Mathematics

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Answer

No real solutions\text{No real solutions}

Step-by-step solution

5 steps
  1. Rewrite the equation using double angle identities.

    The given equation is 2sin⁡(θ)cos⁡(θ)−2cos⁡2(θ)+3=02 \sin(\theta) \cos(\theta) - 2 \cos^2(\theta) + 3 = 0.
    We use the identities:
    sin⁡(2θ)=2sin⁡(θ)cos⁡(θ)\sin(2\theta) = 2 \sin(\theta) \cos(\theta)
    cos⁡(2θ)=2cos⁡2(θ)−1  ⟹  2cos⁡2(θ)=cos⁡(2θ)+1\cos(2\theta) = 2 \cos^2(\theta) - 1 \implies 2 \cos^2(\theta) = \cos(2\theta) + 1

    Substitute these into the equation:

    sin⁡(2θ)−(cos⁡(2θ)+1)+3=0\sin(2\theta) - (\cos(2\theta) + 1) + 3 = 0
  2. Simplify the equation.

    sin⁡(2θ)−cos⁡(2θ)−1+3=0\sin(2\theta) - \cos(2\theta) - 1 + 3 = 0 sin⁡(2θ)−cos⁡(2θ)+2=0\sin(2\theta) - \cos(2\theta) + 2 = 0 sin⁡(2θ)−cos⁡(2θ)=−2\sin(2\theta) - \cos(2\theta) = -2
  3. Express the left side in the form Rsin⁡(A−B)R \sin(A - B).

    For an expression asin⁡(x)+bcos⁡(x)a \sin(x) + b \cos(x), we can write it as Rsin⁡(x+α)R \sin(x + \alpha), where R=a2+b2R = \sqrt{a^2 + b^2}.
    Here, a=1a=1 and b=−1b=-1 for sin⁡(2θ)−cos⁡(2θ)\sin(2\theta) - \cos(2\theta).
    R=12+(−1)2=1+1=2R = \sqrt{1^2 + (-1)^2} = \sqrt{1+1} = \sqrt{2}.
    We want to write sin⁡(2θ)−cos⁡(2θ)\sin(2\theta) - \cos(2\theta) as 2sin⁡(2θ−α)\sqrt{2} \sin(2\theta - \alpha).
    Comparing sin⁡(2θ)−cos⁡(2θ)\sin(2\theta) - \cos(2\theta) with 2(sin⁡(2θ)cos⁡(α)−cos⁡(2θ)sin⁡(α))\sqrt{2}(\sin(2\theta)\cos(\alpha) - \cos(2\theta)\sin(\alpha)), we have:
    2cos⁡(α)=1  ⟹  cos⁡(α)=12\sqrt{2}\cos(\alpha) = 1 \implies \cos(\alpha) = \frac{1}{\sqrt{2}}
    2sin⁡(α)=1  ⟹  sin⁡(α)=12\sqrt{2}\sin(\alpha) = 1 \implies \sin(\alpha) = \frac{1}{\sqrt{2}}
    This implies α=π4\alpha = \frac{\pi}{4} (or 45∘45^\circ).

  4. Substitute this back into the equation.

    2sin⁡(2θ−π4)=−2\sqrt{2} \sin\left(2\theta - \frac{\pi}{4}\right) = -2

    Divide by 2\sqrt{2}:

    sin⁡(2θ−π4)=−22\sin\left(2\theta - \frac{\pi}{4}\right) = \frac{-2}{\sqrt{2}} sin⁡(2θ−π4)=−2\sin\left(2\theta - \frac{\pi}{4}\right) = -\sqrt{2}
  5. Determine the solution.

    The range of the sine function is [−1,1][-1, 1].
    Since −2≈−1.414-\sqrt{2} \approx -1.414, which is less than −1-1, there is no real angle whose sine is −2-\sqrt{2}.
    Therefore, there are no real solutions for θ\theta.

    The final answer is No real solutions\text{No real solutions}.

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