Q. Find all angles, 0∘≤θ<360∘, that satisfy the equation below, to the nearest tenth of a degree.4sec2θ−25=0Answer: θ=
Solve for sec(θ): Solve the equation for sec(θ). 4sec2(θ)−25=0 Add 25 to both sides. 4sec2(θ)=25 Divide both sides by 4. sec2(θ)=425 Take the square root of both sides. sec(θ)=±425 sec(θ)=±25
Find cosine values: Find the corresponding cosine values since sec(θ) is the reciprocal of cos(θ).sec(θ)=cos(θ)1cos(θ)=sec(θ)1cos(θ)=±52
Determine cosine quadrants: Determine the quadrants where cosine is positive and negative.Cosine is positive in the first and fourth quadrants and negative in the second and third quadrants.
Principal angle for positive cosine: Use the inverse cosine function to find the principal angle for the positive cosine value. θ=cos−1(52)Calculate the principal angle.θ≈cos−1(0.4)θ≈66.4∘
Second angle for positive cosine: Find the second angle in the first cycle (0∘ to 360∘) where cosine is positive.Since cosine is also positive in the fourth quadrant, the second angle is 360∘−66.4∘.θ≈360∘−66.4∘θ≈293.6∘
Principal angle for negative cosine: Use the inverse cosine function to find the principal angle for the negative cosine value.θ=cos−1(−52)Calculate the principal angle.θ≈cos−1(−0.4)θ≈113.6∘
Second angle for negative cosine: Find the second angle in the first cycle (0∘ to 360∘) where cosine is negative.Since cosine is also negative in the third quadrant, the second angle is 180∘+(180∘−113.6∘).θ≈180∘+(180∘−113.6∘)θ≈180∘+66.4∘θ≈246.4∘
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