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Find all angles, 
0^(@) <= theta < 360^(@), that satisfy the equation below, to the nearest tenth of a degree.

9cos^(2)theta+3cos theta=8cos theta+4
Answer: 
theta=

Find all angles, 0^{\circ} \leq \theta<360^{\circ} , that satisfy the equation below, to the nearest tenth of a degree.\newline9cos2θ+3cosθ=8cosθ+4 9 \cos ^{2} \theta+3 \cos \theta=8 \cos \theta+4 \newlineAnswer: θ= \theta=

Full solution

Q. Find all angles, 0θ<360 0^{\circ} \leq \theta<360^{\circ} , that satisfy the equation below, to the nearest tenth of a degree.\newline9cos2θ+3cosθ=8cosθ+4 9 \cos ^{2} \theta+3 \cos \theta=8 \cos \theta+4 \newlineAnswer: θ= \theta=
  1. Rewrite Equation: Rewrite the given equation to collect all terms on one side and set the equation to zero.\newline9cos2(θ)+3cos(θ)8cos(θ)4=09\cos^2(\theta) + 3\cos(\theta) - 8\cos(\theta) - 4 = 0\newlineSimplify the equation by combining like terms.\newline9cos2(θ)5cos(θ)4=09\cos^2(\theta) - 5\cos(\theta) - 4 = 0
  2. Simplify Equation: Factor the quadratic equation in terms of cos(θ)\cos(\theta).$9cos2(θ)5cos(θ)4\$9\cos^2(\theta) - 5\cos(\theta) - 4 = 3cos(θ)+13\cos(\theta) + 13cos(θ)43\cos(\theta) - 4\)Set each factor equal to zero to find the values of cos(θ)\cos(\theta).3cos(θ)+1=03\cos(\theta) + 1 = 0 and 3cos(θ)4=03\cos(\theta) - 4 = 0
  3. Factor Quadratic Equation: Solve each equation for cos(θ)\cos(\theta). For 3cos(θ)+1=03\cos(\theta) + 1 = 0: cos(θ)=13\cos(\theta) = -\frac{1}{3} For 3cos(θ)4=03\cos(\theta) - 4 = 0: cos(θ)=43\cos(\theta) = \frac{4}{3} However, since the cosine of an angle cannot be greater than 11, cos(θ)=43\cos(\theta) = \frac{4}{3} is not a valid solution.
  4. Solve for cos(θ)\cos(\theta): Find the angles θ\theta that correspond to cos(θ)=13\cos(\theta) = -\frac{1}{3} in the range 0^\circ \leq \theta < 360^\circ. Use the inverse cosine function and consider the symmetry of the cosine function, which is positive in the first and fourth quadrants and negative in the second and third quadrants. θ=cos1(13)\theta = \cos^{-1}(-\frac{1}{3}) Calculate the principal value. θcos1(13)109.5\theta \approx \cos^{-1}(-\frac{1}{3}) \approx 109.5^\circ
  5. Find θ\theta for cos(θ)=13\cos(\theta) = -\frac{1}{3}: Find the second angle in the range 0^\circ \leq \theta < 360^\circ that also has a cosine of 13-\frac{1}{3}.\newlineSince cosine is negative in the second and third quadrants, the second angle is the supplement of the principal value.\newlineθ=180+(180109.5)\theta = 180^\circ + (180^\circ - 109.5^\circ)\newlineθ180+70.5\theta \approx 180^\circ + 70.5^\circ\newlineθ250.5\theta \approx 250.5^\circ

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