Find all angles, 0^{\circ} \leq \theta<360^{\circ} , that satisfy the equation below, to the nearest tenth of a degree.−4cos2θ+13cosθ−5=9cosθ−8Answer: θ=
Q. Find all angles, 0∘≤θ<360∘, that satisfy the equation below, to the nearest tenth of a degree.−4cos2θ+13cosθ−5=9cosθ−8Answer: θ=
Rewrite Equation: First, let's rewrite the given equation to collect like terms on one side:−4cos2(θ)+13cos(θ)−5=9cos(θ)−8
Combine Like Terms: Now, subtract 9cos(θ) from both sides and add 8 to both sides to get all terms involving cos(θ) on one side and the constant on the other side:−4cos2(θ)+13cos(θ)−5−9cos(θ)+8=0
Quadratic Equation: Simplify the equation by combining like terms: −4cos2(θ)+4cos(θ)+3=0
Factorize: This is a quadratic equation in terms of cos(θ). Let's set u=cos(θ) to make it easier to solve:−4u2+4u+3=0
Solve for u: Now, we can factor the quadratic equation:−4u2+4u+3=0(2u+1)(−2u+3)=0
Find Possible Values: Set each factor equal to zero and solve for u:2u+1=0 or −2u+3=0
Discard Invalid Value: Solve the first equation for u:2u+1=02u=−1u=−21
Find Corresponding Angles: Solve the second equation for u:\(\newline\)−2u + 3 = 0\(\newline\)−2u = −3\(\newline\)u = 23
Final Answer: Since u=cos(θ), we have two possible values for cos(θ): −21 and 23. However, the cosine of an angle cannot be greater than 1, so we discard the value 23.
Final Answer: Since u=cos(θ), we have two possible values for cos(θ): −21 and 23. However, the cosine of an angle cannot be greater than 1, so we discard the value 23.Now we find the angles θ that correspond to cos(θ)=−21. The cosine of −21 occurs at 120 degrees and cos(θ)0 degrees in the range of cos(θ)1 to cos(θ)2 degrees.
Final Answer: Since u=cos(θ), we have two possible values for cos(θ): −21 and 23. However, the cosine of an angle cannot be greater than 1, so we discard the value 23.Now we find the angles θ that correspond to cos(θ)=−21. The cosine of −21 occurs at 120 degrees and cos(θ)0 degrees in the range of cos(θ)1 to cos(θ)2 degrees.We can now write the final answer with the angles that satisfy the original equation:cos(θ)3 degrees, cos(θ)0 degrees
More problems from Find the roots of factored polynomials