Q. Find all angles, 0∘≤θ<360∘, that satisfy the equation below, to the nearest tenth of a degree.9sin2θ+sinθ=−2sinθ+2Answer: θ=
Simplify Equation: Simplify the given equation by moving all terms to one side to set the equation to zero.9sin2θ+sinθ=−2sinθ+2Add 2sinθ to both sides and subtract 2 from both sides to get:9sin2θ+3sinθ−2=0
Factor Quadratic Equation: Factor the quadratic equation in terms of sinθ. We are looking for two numbers that multiply to (9)(−2)=−18 and add up to 3. These numbers are 6 and −3. So we can write the equation as: (3sinθ−2)(3sinθ+1)=0
Solve First Factor: Solve each factor for sinθ.First factor: 3sinθ−2=0Add 2 to both sides:3sinθ=2Divide by 3:sinθ=32
Solve Second Factor: Solve the second factor for sinθ.Second factor: 3sinθ+1=0Subtract 1 from both sides:3sinθ=−1Divide by 3:sinθ=−31
Find Angle for sin(32): Find the angles that correspond to sinθ=32. Since sinθ=32 is not a standard angle, we will use a calculator to find the inverse sine (arcsin) of 32. θ=arcsin(32) This will give us the principal angle in the first quadrant. We also need to find the angle in the second quadrant where sine is positive. θ1=arcsin(32)≈41.8∘θ2=180∘−θ1≈180∘−41.8∘≈138.2∘
Find Angle for sin(−31): Find the angles that correspond to sinθ=−31.Since sinθ=−31 is also not a standard angle, we will use a calculator to find the inverse sine (arcsin) of −31.θ=arcsin(−31)This will give us the principal angle in the fourth quadrant. We also need to find the angle in the third quadrant where sine is negative.θ3=360°−arcsin(31)≈360°−19.5°≈340.5°θ4=180°+arcsin(31)≈180°+19.5°≈199.5°
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