Math Problem Statement

sin(arccos(-1/3))

Solution

To evaluate sin(arccos(1/3))\sin(\arccos(-1/3)), we can follow these steps:

Step 1: Understanding the Problem

We are asked to find the sine of the angle whose cosine is 13-\frac{1}{3}.

Let: θ=arccos(13)\theta = \arccos\left(-\frac{1}{3}\right) This means: cos(θ)=13\cos(\theta) = -\frac{1}{3} Now, we need to find sin(θ)\sin(\theta).

Step 2: Use the Pythagorean Identity

The Pythagorean identity states that: sin2(θ)+cos2(θ)=1\sin^2(\theta) + \cos^2(\theta) = 1 We already know cos(θ)=13\cos(\theta) = -\frac{1}{3}, so we can plug this value into the identity: sin2(θ)+(13)2=1\sin^2(\theta) + \left(-\frac{1}{3}\right)^2 = 1 sin2(θ)+19=1\sin^2(\theta) + \frac{1}{9} = 1 sin2(θ)=119=9919=89\sin^2(\theta) = 1 - \frac{1}{9} = \frac{9}{9} - \frac{1}{9} = \frac{8}{9}

Step 3: Solve for sin(θ)\sin(\theta)

Now, take the square root of both sides: sin(θ)=±89=±83=±223\sin(\theta) = \pm \sqrt{\frac{8}{9}} = \pm \frac{\sqrt{8}}{3} = \pm \frac{2\sqrt{2}}{3}

Step 4: Determine the Sign of sin(θ)\sin(\theta)

Since arccos(x)\arccos(x) returns values in the range [0,π][0, \pi], where sine is always non-negative, we take the positive value: sin(θ)=223\sin(\theta) = \frac{2\sqrt{2}}{3}

Final Answer:

sin(arccos(1/3))=223\sin(\arccos(-1/3)) = \frac{2\sqrt{2}}{3}

Would you like further clarification on any of the steps, or do you have another question?

Additional Questions:

  1. What is the value of cos(arcsin(x))\cos(\arcsin(x))?
  2. How can we derive the Pythagorean identity?
  3. What is the general form of sin(arccos(x))\sin(\arccos(x)) for any xx?
  4. Can you explain the relationship between the range of the arccosine function and the sign of sine?
  5. How can you calculate tan(arcsin(x))\tan(\arcsin(x))?

Tip: To remember the relationship between the inverse trigonometric functions and the Pythagorean identity, think of the right triangle formed by the sine and cosine values and use the identity sin2(θ)+cos2(θ)=1\sin^2(\theta) + \cos^2(\theta) = 1 to solve for the unknown.

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Math Problem Analysis

Mathematical Concepts

Trigonometry
Inverse Trigonometric Functions
Pythagorean Identity

Formulas

sin^2(θ) + cos^2(θ) = 1
sin(θ) = ±√(1 - cos^2(θ))

Theorems

Pythagorean identity
Inverse trigonometric function properties

Suitable Grade Level

Grades 9-11