Math Problem Statement

Solve the equation for solutions over the interval ​[0degrees​, 360degrees​). cotangent theta plus 3 cosecant thetaequals5

Solution

We are given the trigonometric equation:

cot(θ)+3csc(θ)=5\cot(\theta) + 3 \csc(\theta) = 5

We will solve this over the interval [0,360][0^\circ, 360^\circ].

Step 1: Express cot(θ)\cot(\theta) and csc(θ)\csc(\theta) in terms of sin(θ)\sin(\theta) and cos(θ)\cos(\theta)

We know that: cot(θ)=cos(θ)sin(θ),csc(θ)=1sin(θ)\cot(\theta) = \frac{\cos(\theta)}{\sin(\theta)}, \quad \csc(\theta) = \frac{1}{\sin(\theta)}

Substitute these into the equation:

cos(θ)sin(θ)+31sin(θ)=5\frac{\cos(\theta)}{\sin(\theta)} + 3 \cdot \frac{1}{\sin(\theta)} = 5

Step 2: Combine terms over a common denominator

The left-hand side has a common denominator of sin(θ)\sin(\theta), so we can rewrite the equation as:

cos(θ)+3sin(θ)=5\frac{\cos(\theta) + 3}{\sin(\theta)} = 5

Step 3: Multiply both sides by sin(θ)\sin(\theta) (assuming sin(θ)0\sin(\theta) \neq 0)

This simplifies to:

cos(θ)+3=5sin(θ)\cos(\theta) + 3 = 5 \sin(\theta)

Step 4: Solve for cos(θ)\cos(\theta)

Rearrange the equation:

cos(θ)=5sin(θ)3\cos(\theta) = 5 \sin(\theta) - 3

Step 5: Use a trigonometric identity

Square both sides to eliminate θ\theta:

cos2(θ)=(5sin(θ)3)2\cos^2(\theta) = (5 \sin(\theta) - 3)^2

Since cos2(θ)+sin2(θ)=1\cos^2(\theta) + \sin^2(\theta) = 1, substitute cos2(θ)\cos^2(\theta):

1sin2(θ)=(5sin(θ)3)21 - \sin^2(\theta) = (5 \sin(\theta) - 3)^2

Step 6: Solve the quadratic equation

Expand the right-hand side:

1sin2(θ)=25sin2(θ)30sin(θ)+91 - \sin^2(\theta) = 25 \sin^2(\theta) - 30 \sin(\theta) + 9

Simplify:

125sin2(θ)+sin2(θ)=930sin(θ)1 - 25 \sin^2(\theta) + \sin^2(\theta) = 9 - 30 \sin(\theta)

125sin2(θ)=930sin(θ)1 - 25 \sin^2(\theta) = 9 - 30 \sin(\theta)

This simplifies to a quadratic equation:

26sin2(θ)30sin(θ)+8=026 \sin^2(\theta) - 30 \sin(\theta) + 8 = 0

Now solve this quadratic equation using the quadratic formula:

sin(θ)=(30)±(30)24(26)(8)2(26)\sin(\theta) = \frac{-(-30) \pm \sqrt{(-30)^2 - 4(26)(8)}}{2(26)}

sin(θ)=30±90083252\sin(\theta) = \frac{30 \pm \sqrt{900 - 832}}{52}

sin(θ)=30±6852\sin(\theta) = \frac{30 \pm \sqrt{68}}{52}

sin(θ)=30±8.246252\sin(\theta) = \frac{30 \pm 8.2462}{52}

Thus:

sin(θ)=30+8.246252orsin(θ)=308.246252\sin(\theta) = \frac{30 + 8.2462}{52} \quad \text{or} \quad \sin(\theta) = \frac{30 - 8.2462}{52}

sin(θ)0.7364orsin(θ)0.4172\sin(\theta) \approx 0.7364 \quad \text{or} \quad \sin(\theta) \approx 0.4172

Step 7: Solve for θ\theta

Now, solve for θ\theta by finding the angles where sin(θ)\sin(\theta) takes these values in the interval [0,360][0^\circ, 360^\circ].

  1. For sin(θ)0.7364\sin(\theta) \approx 0.7364: θsin1(0.7364)47.54(1st quadrant)\theta \approx \sin^{-1}(0.7364) \approx 47.54^\circ \quad \text{(1st quadrant)} The second solution in the 2nd quadrant: θ18047.54=132.46\theta \approx 180^\circ - 47.54^\circ = 132.46^\circ

  2. For sin(θ)0.4172\sin(\theta) \approx 0.4172: θsin1(0.4172)24.64(1st quadrant)\theta \approx \sin^{-1}(0.4172) \approx 24.64^\circ \quad \text{(1st quadrant)} The second solution in the 2nd quadrant: θ18024.64=155.36\theta \approx 180^\circ - 24.64^\circ = 155.36^\circ

Final Answer

The solutions are:

θ47.54,132.46,24.64,155.36\theta \approx 47.54^\circ, 132.46^\circ, 24.64^\circ, 155.36^\circ

Let me know if you'd like more details or have any questions!


Related questions:

  1. How do you solve trigonometric equations involving both sine and cosine?
  2. What is the general form of the quadratic formula?
  3. How can you use trigonometric identities to simplify equations?
  4. What are the key steps for solving quadratic equations?
  5. How do inverse trigonometric functions work?

Tip: Always check the domain and range of trigonometric functions when solving equations to ensure solutions are within the required interval.

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Math Problem Analysis

Mathematical Concepts

Trigonometry
Trigonometric Identities
Quadratic Equations

Formulas

cot(θ) = cos(θ)/sin(θ)
csc(θ) = 1/sin(θ)
Pythagorean identity: sin^2(θ) + cos^2(θ) = 1
Quadratic formula: (-b ± √(b^2 - 4ac)) / 2a

Theorems

Pythagorean Identity
Quadratic Formula

Suitable Grade Level

Grades 10-12