Math Problem Statement

Cot theta=-2/8,cos theta<0, find sin theta

Solution

We are given that:

cot(θ)=28=14\cot(\theta) = -\frac{2}{8} = -\frac{1}{4}

and

cos(θ)<0.\cos(\theta) < 0.

To find sin(θ)\sin(\theta), let's proceed step by step:

Step 1: Find tan(θ)\tan(\theta)

We know that:

cot(θ)=1tan(θ)\cot(\theta) = \frac{1}{\tan(\theta)}

So,

tan(θ)=4.\tan(\theta) = -4.

Step 2: Use the identity involving sin(θ)\sin(\theta) and cos(θ)\cos(\theta)

The identity for tan(θ)\tan(\theta) is:

tan(θ)=sin(θ)cos(θ).\tan(\theta) = \frac{\sin(\theta)}{\cos(\theta)}.

Thus, we have:

4=sin(θ)cos(θ).-4 = \frac{\sin(\theta)}{\cos(\theta)}.

This gives us the relation:

sin(θ)=4cos(θ).\sin(\theta) = -4 \cos(\theta).

Step 3: Apply the Pythagorean identity

Using the fundamental identity:

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

we substitute sin(θ)=4cos(θ)\sin(\theta) = -4 \cos(\theta) into this equation:

(4cos(θ))2+cos2(θ)=1,(-4 \cos(\theta))^2 + \cos^2(\theta) = 1,

which simplifies to:

16cos2(θ)+cos2(θ)=1,16 \cos^2(\theta) + \cos^2(\theta) = 1,

17cos2(θ)=1,17 \cos^2(\theta) = 1,

cos2(θ)=117.\cos^2(\theta) = \frac{1}{17}.

Step 4: Solve for cos(θ)\cos(\theta)

Since we are told that cos(θ)<0\cos(\theta) < 0, we take the negative square root:

cos(θ)=117.\cos(\theta) = -\frac{1}{\sqrt{17}}.

Step 5: Find sin(θ)\sin(\theta)

Now, substitute cos(θ)\cos(\theta) into the equation sin(θ)=4cos(θ)\sin(\theta) = -4 \cos(\theta):

sin(θ)=4(117),\sin(\theta) = -4 \left(-\frac{1}{\sqrt{17}}\right),

sin(θ)=417.\sin(\theta) = \frac{4}{\sqrt{17}}.

Thus, the value of sin(θ)\sin(\theta) is:

sin(θ)=417.\sin(\theta) = \frac{4}{\sqrt{17}}.


Would you like more details on any of these steps or have any questions? Here are some related questions for practice:

  1. If sin(θ)=417\sin(\theta) = \frac{4}{\sqrt{17}}, find cos(θ)\cos(\theta).
  2. Given tan(θ)=4\tan(\theta) = -4, what is the value of sec(θ)\sec(\theta)?
  3. If sin(θ)=417\sin(\theta) = \frac{4}{\sqrt{17}}, what is the value of csc(θ)\csc(\theta)?
  4. Find the exact value of sin(2θ)\sin(2\theta) given cot(θ)=14\cot(\theta) = -\frac{1}{4}.
  5. What quadrant is θ\theta located in if cos(θ)<0\cos(\theta) < 0 and cot(θ)<0\cot(\theta) < 0?

Tip: Always determine the correct quadrant based on given information to ensure the correct sign of trigonometric functions.

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Math Problem Analysis

Mathematical Concepts

Trigonometry
Trigonometric Ratios
Pythagorean Identity

Formulas

cot(θ) = 1/tan(θ)
sin²(θ) + cos²(θ) = 1
tan(θ) = sin(θ)/cos(θ)

Theorems

Pythagorean Identity: sin²(θ) + cos²(θ) = 1

Suitable Grade Level

Grades 10-12