Q. Find all angles, 0∘≤θ<360∘, that satisfy the equation below, to the nearest tenth of a degree.−6cos2θ−5cosθ=1Answer: θ=
Rewrite Equation: Let's first rewrite the equation in a more familiar quadratic form by substituting cos(θ) with a variable, let's say 'x'. So the equation becomes:−6x2−5x=1Now, we need to solve for 'x' before we can find the corresponding angles for θ.
Solve Quadratic Equation: To solve the quadratic equation, we first move all terms to one side to set the equation to zero:−6x2−5x−1=0Now, we can use the quadratic formula to find the solutions for 'x'. The quadratic formula is x=2a−b±b2−4ac, where a=−6, b=−5, and c=−1.
Calculate Discriminant: Let's calculate the discriminant (b2−4ac) first:Discriminant = (−5)2−4(−6)(−1)=25−24=1Since the discriminant is positive, we will have two real solutions for ′x′.
Find Solutions for x: Now, we can find the two solutions for 'x' using the quadratic formula:x=2⋅−6−(−5)±1x=−125±1This gives us two solutions for 'x':x1=−125+1=−126=−0.5x2=−125−1=−124=−31
Find Angles for x1: Now we need to find the angles θ that correspond to the cosine values of x1 and x2. Since we are looking for angles between 0 and 360 degrees, we will use the inverse cosine function and also consider the symmetry of the cosine function.For x1=−0.5, we find the related angle:θ1=cos−1(−0.5)
Calculate θ1 and θ2: Using a calculator, we find:θ1=cos−1(−0.5)≈120 degreesHowever, since cosine is positive in the fourth quadrant as well, we also have another angle:θ2=360−θ1≈360−120=240 degrees
Find Angles for x2: For x2=−31, we find the related angle:θ3=cos−1(−31)Using a calculator, we find:θ3≈cos−1(−31)≈109.5 degrees (to the nearest tenth)Again, considering the symmetry of the cosine function, we find another angle:θ4=360−θ3≈360−109.5=250.5 degrees (to the nearest tenth)
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