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2 sin(5θ) cos(5θ) - 2 cos²(5θ) + 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⁡(5θ)cos⁡(5θ)−2cos⁡2(5θ)+3=02 \sin(5\theta) \cos(5\theta) - 2 \cos^2(5\theta) + 3 = 0.
    We use the identities:
    sin⁡(2x)=2sin⁡(x)cos⁡(x)\sin(2x) = 2 \sin(x) \cos(x)
    cos⁡(2x)=2cos⁡2(x)−1  ⟹  2cos⁡2(x)=cos⁡(2x)+1\cos(2x) = 2 \cos^2(x) - 1 \implies 2 \cos^2(x) = \cos(2x) + 1

    Substitute these into the equation, with x=5θx = 5\theta:

    sin⁡(2⋅5θ)−(cos⁡(2⋅5θ)+1)+3=0\sin(2 \cdot 5\theta) - (\cos(2 \cdot 5\theta) + 1) + 3 = 0 sin⁡(10θ)−(cos⁡(10θ)+1)+3=0\sin(10\theta) - (\cos(10\theta) + 1) + 3 = 0
  2. Simplify the equation.

    sin⁡(10θ)−cos⁡(10θ)−1+3=0\sin(10\theta) - \cos(10\theta) - 1 + 3 = 0 sin⁡(10θ)−cos⁡(10θ)+2=0\sin(10\theta) - \cos(10\theta) + 2 = 0 sin⁡(10θ)−cos⁡(10θ)=−2\sin(10\theta) - \cos(10\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⁡(10θ)−cos⁡(10θ)\sin(10\theta) - \cos(10\theta).
    R=12+(−1)2=1+1=2R = \sqrt{1^2 + (-1)^2} = \sqrt{1+1} = \sqrt{2}.
    We want to write sin⁡(10θ)−cos⁡(10θ)\sin(10\theta) - \cos(10\theta) as 2sin⁡(10θ−α)\sqrt{2} \sin(10\theta - \alpha).
    Comparing sin⁡(10θ)−cos⁡(10θ)\sin(10\theta) - \cos(10\theta) with 2(sin⁡(10θ)cos⁡(α)−cos⁡(10θ)sin⁡(α))\sqrt{2}(\sin(10\theta)\cos(\alpha) - \cos(10\theta)\sin(\alpha)), we find cos⁡(α)=12\cos(\alpha) = \frac{1}{\sqrt{2}} and sin⁡(α)=12\sin(\alpha) = \frac{1}{\sqrt{2}}.
    This implies α=π4\alpha = \frac{\pi}{4}.

  4. Substitute this back into the equation.

    2sin⁡(10θ−π4)=−2\sqrt{2} \sin\left(10\theta - \frac{\pi}{4}\right) = -2

    Divide by 2\sqrt{2}:

    sin⁡(10θ−π4)=−22\sin\left(10\theta - \frac{\pi}{4}\right) = \frac{-2}{\sqrt{2}} sin⁡(10θ−π4)=−2\sin\left(10\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\boxed{\text{No real solutions}}.
    2 zimekamilika. Zimebaki 3 leo — tuma inayofuata.

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