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

-2cos^(2)theta-3cos theta=1
Answer: 
theta=

Find all angles, 0θ<360 0^{\circ} \leq \theta<360^{\circ} , that satisfy the equation below, to the nearest tenth of a degree.\newline2cos2θ3cosθ=1 -2 \cos ^{2} \theta-3 \cos \theta=1 \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.\newline2cos2θ3cosθ=1 -2 \cos ^{2} \theta-3 \cos \theta=1 \newlineAnswer: θ= \theta=
  1. Rewrite Equation with Variable: Let's first rewrite the equation in a more standard quadratic form by substituting cos(θ)\cos(\theta) with a variable, let's say 'xx'. So, we have 2x23x=1-2x^2 - 3x = 1.
  2. Set Equation to Zero: To solve for 'x', we need to set the equation to zero. So, we add 11 to both sides of the equation to get 2x23x+1=0-2x^2 - 3x + 1 = 0.
  3. Solve Quadratic Equation: Now, we need to solve the quadratic equation 2x23x+1=0-2x^2 - 3x + 1 = 0. We can use the quadratic formula, x=b±b24ac2ax = \frac{-b \pm \sqrt{b^2 - 4ac}}{2a}, where a=2a = -2, b=3b = -3, and c=1c = 1.
  4. Calculate Discriminant: First, we calculate the discriminant, which is b24acb^2 - 4ac. Plugging in the values, we get (3)24(2)(1)=9+8=17(-3)^2 - 4(-2)(1) = 9 + 8 = 17.
  5. Find First Solution: Now, we can find the two solutions for 'x' using the quadratic formula. The first solution is x=(3)+1722=3+174x = \frac{-(-3) + \sqrt{17}}{2 \cdot -2} = \frac{3 + \sqrt{17}}{-4}.
  6. Find Second Solution: The second solution for 'x' is x=(3)1722=3174x = \frac{-(-3) - \sqrt{17}}{2 \cdot -2} = \frac{3 - \sqrt{17}}{-4}.
  7. Check Validity of Solutions: We need to check if these solutions for 'x' are within the range of the cosine function, which is between 1-1 and 11. Let's calculate the numerical values: x1=(3+17)/4x_1 = (3 + \sqrt{17}) / -4 and x2=(317)/4x_2 = (3 - \sqrt{17}) / -4.
  8. Calculate Angle for x2x_2: Calculating the values, we get x11.28x_1 \approx -1.28 (which is not possible since the range of cosine is between 1-1 and 11) and x20.28x_2 \approx 0.28.
  9. Find Second Angle: Since x1x_1 is not within the range of cosine, we discard it. Now, we need to find the angles θ\theta for which cos(θ)=x20.28\cos(\theta) = x_2 \approx 0.28. We will use the inverse cosine function to find these angles.
  10. Final Angles: Using a calculator, we find that cos1(0.28)\cos^{-1}(0.28) gives us the principal value of θ\theta, which is approximately 73.773.7 degrees.
  11. Final Angles: Using a calculator, we find that cos1(0.28)\cos^{-1}(0.28) gives us the principal value of θ\theta, which is approximately 73.773.7 degrees.However, since the cosine function is positive in both the first and fourth quadrants, we need to find the second angle by subtracting the principal value from 360360 degrees. So, 36073.7=286.3360 - 73.7 = 286.3 degrees.
  12. Final Angles: Using a calculator, we find that cos1(0.28)\cos^{-1}(0.28) gives us the principal value of θ\theta, which is approximately 73.773.7 degrees. However, since the cosine function is positive in both the first and fourth quadrants, we need to find the second angle by subtracting the principal value from 360360 degrees. So, 36073.7=286.3360 - 73.7 = 286.3 degrees. We now have two angles that satisfy the original equation: θ73.7\theta \approx 73.7 degrees and θ286.3\theta \approx 286.3 degrees. These are the angles between 00 and 360360 degrees that satisfy the equation 2cos2(θ)3cos(θ)=1-2\cos^2(\theta) - 3\cos(\theta) = 1.

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