Homework

Given a point P on the unit circle at an angle of \( \theta = \frac{3\pi}{4} \), find the coordinates of point P Then, determine the value of \( \cos(2\theta) \) and \( \sin(2\theta) \)

When $ \theta = \frac{3\pi}{4} $, the coordinates of point P on the unit circle are given by $ (\cos(\theta), \sin(\theta)) $.

First, we need to calculate these values:

$$ \cos \left( \frac{3\pi}{4} \right) = -\frac{\sqrt{2}}{2} $$

$$ \sin \left( \frac{3\pi}{4} \right) = \frac{\sqrt{2}}{2} $$

So, the coordinates of point P are $ \left( -\frac{\sqrt{2}}{2}, \frac{\sqrt{2}}{2} \right) $.

Next, we determine $ \cos(2\theta) $ and $ \sin(2\theta) $ using the double-angle formulas:

$$ \cos(2\theta) = \cos(2 \cdot \frac{3\pi}{4}) = \cos \left( \frac{6\pi}{4} \right) = \cos \left( \frac{3\pi}{2} \right) = 0 $$

$$ \sin(2\theta) = \sin(2 \cdot \frac{3\pi}{4}) = \sin \left( \frac{6\pi}{4} \right) = \sin \left( \frac{3\pi}{2} \right) = -1 $$

Find the coordinates of the point on the unit circle corresponding to an angle of \( \frac{5\pi}{4} \) radians

To find the coordinates of the point on the unit circle corresponding to the angle $ \frac{5\pi}{4} $ radians, we need to use the unit circle properties.

The angle $ \frac{5\pi}{4} $ radians is in the third quadrant.

The reference angle for $ \frac{5\pi}{4} $ is $ \pi/4 $ radians.

In the third quadrant, both sine and cosine values are negative.

From the unit circle, we know:

$$ \cos \left( \frac{\pi}{4} \right) = \frac{\sqrt{2}}{2} $$

$$ \sin \left( \frac{\pi}{4} \right) = \frac{\sqrt{2}}{2} $$

Therefore, the coordinates for $ \frac{5\pi}{4} $ are:

$$ \left( -\frac{\sqrt{2}}{2}, -\frac{\sqrt{2}}{2} \right) $$

Find the exact values of the cosine and sine for three points on the unit circle

Given points on the unit circle: $\frac{\pi}{6}, \frac{5\pi}{4}, \frac{11\pi}{6}$, find the exact values of $\cos$ and $\sin$.

Prove the relationship between the sine and cosine of the sum of two angles using the unit circle

To prove the relationship between the sine and cosine of the sum of two angles, we use the unit circle and the definitions of sine and cosine:

Given two angles, $\alpha$ and $\beta$, we can represent their sums on the unit circle. Consider the points $(\cos(\alpha), \sin(\alpha))$ and $(\cos(\beta), \sin(\beta))$.

Using the unit circle and the angle addition formulas, we have:

$$ \cos(\alpha + \beta) = \cos(\alpha) \cos(\beta) – \sin(\alpha) \sin(\beta) $$

$$ \sin(\alpha + \beta) = \sin(\alpha) \cos(\beta) + \cos(\alpha) \sin(\beta) $$

These relationships can be derived by examining the projections of the points on the unit circle and considering the definitions of sine and cosine in terms of coordinates.

Find the cosine and sine of an angle on the unit circle at \(\frac{5\pi}{6}\) radians

To find the cosine and sine values for $\frac{5\pi}{6}$ radians, first recognize that $\frac{5\pi}{6}$ is in the second quadrant of the unit circle.

In the second quadrant, sine is positive and cosine is negative.

Next, find the reference angle for $\frac{5\pi}{6}$, which is $\pi – \frac{5\pi}{6} = \frac{\pi}{6}$.

We know the sine and cosine values for the angle $\frac{\pi}{6}$:

$$\sin\left( \frac{\pi}{6} \right) = \frac{1}{2}$$

$$\cos\left( \frac{\pi}{6} \right) = \frac{\sqrt{3}}{2}$$

Since $\frac{5\pi}{6}$ is in the second quadrant, the cosine value will be negative.

Therefore:

$$\sin\left( \frac{5\pi}{6} \right) = \frac{1}{2}$$

$$\cos\left( \frac{5\pi}{6} \right) = -\frac{\sqrt{3}}{2}$$

If the standard unit circle is flipped over the x-axis, describe the transformation of the angle θ and calculate the new coordinates for θ = 2π/3

When the unit circle is flipped over the x-axis, the y-coordinates of all points on the circle are inverted. Therefore, the angle $\theta$ remains the same in magnitude but the y-value of the coordinate changes sign.

For $\theta = \frac{2\pi}{3}$, the original coordinates on the unit circle are:

$$\left(\cos\left(\frac{2\pi}{3}\right), \sin\left(\frac{2\pi}{3}\right)\right)$$

We compute:

$$\cos\left(\frac{2\pi}{3}\right) = -\frac{1}{2}$$

$$\sin\left(\frac{2\pi}{3}\right) = \frac{\sqrt{3}}{2}$$

Therefore, the original coordinates are:
$$\left(-\frac{1}{2}, \frac{\sqrt{3}}{2}\right)$$

After flipping over the x-axis, the new coordinates become:
$$\left(-\frac{1}{2}, -\frac{\sqrt{3}}{2}\right)$$

Find the angle θ in the unit circle such that cos(θ) = -1/2

We know that $ \cos(\theta) = -\frac{1}{2} $.

This value of cosine corresponds to two angles in the unit circle, which are in the second and third quadrants.

In the second quadrant, the reference angle is $ \theta = \pi – \frac{\pi}{3} = \frac{2\pi}{3} $.

In the third quadrant, the reference angle is $ \theta = \pi + \frac{\pi}{3} = \frac{4\pi}{3} $.

Therefore, $ \theta = \frac{2\pi}{3} $ or $ \theta = \frac{4\pi}{3} $.

Suppose that angle θ is positioned on the unit circle such that θ = 5π/6 Determine the coordinates of the point where the terminal side of θ intersects the unit circle

First, we identify that $ \theta = \frac{5\pi}{6} $ is in the second quadrant. The reference angle is $ \pi – \frac{5\pi}{6} = \frac{\pi}{6} $.

In the unit circle, the cosine and sine of $ \frac{\pi}{6} $ are $ \frac{\sqrt{3}}{2} $ and $ \frac{1}{2} $, respectively.

Therefore, in the second quadrant, the coordinates are $ (-\frac{\sqrt{3}}{2}, \frac{1}{2}) $.

$$ \text{Coordinates: } \left(-\frac{\sqrt{3}}{2}, \frac{1}{2}\right) $$

How to Find the Reference Angle Not on Unit Circle

To find the reference angle of an angle not on the unit circle, follow these steps:

1. Determine the quadrant in which the angle is located.

2. Use the following rules based on the quadrant to find the reference angle:

For an angle $\theta$ in the first quadrant, the reference angle is $\theta$.

For an angle $\theta$ in the second quadrant, the reference angle is $180^\circ – \theta$.

For an angle $\theta$ in the third quadrant, the reference angle is $\theta – 180^\circ$.

For an angle $\theta$ in the fourth quadrant, the reference angle is $360^\circ – \theta$.

Example: Find the reference angle for $210^\circ$.

Since $210^\circ$ is in the third quadrant, we use the rule for the third quadrant:

$$\text{Reference Angle} = 210^\circ – 180^\circ = 30^\circ$$

Therefore, the reference angle for $210^\circ$ is $30^\circ$.