1. Why is cosine positive in the 4th quadrant and sine isn't?
Your answer
2. An angle measures 120 degrees. Describe how to use special right triangles
and the unit circle as tools to calculate the sine and cosine of this angle.
Your answer
3. Explain why you cannot use the Distributive Property to evaluate an expression
in the form of sin(a + b). Please illustrate with an example along with your
explanation
Your answer

because cosine dependency on sine - 1

Step-by-step explanation:

The unit circle has a radius of one, so the hypotenuse is 1. Sine is opposite over hypotenuse. Since the hypotenuse is 1, sine on the unit circle is the opposite side. When you look at the unit circle, the opposite side is perpendicular to the x-axis. This means that, essentially, the opposite side is the height from, or the distance from, the x-axis, which is the y-value.

a unit circle (a circle with radius one), is that if you draw a right triangle where the hypotenuse of the triangle connects a point on the unit circle with the point (0, 0), the length of the hypotenuse is always going to be one. Because that's the radius of the circle! And the length of the other two sides are just going to be the x and y coordinates of the point on the unit circle.

Take a little time drawing right triangles were the hypotenuse connects the middle of the unit circle to a point on the circle and see if you can convince yourself that this is the case.

So you have a right triangle where one side length is the x-coordinate and one side length is the y-coordinate, and the hypotenuse is equal to 1. This means you can figure out the sine and cosine of the angle that the hypotenuse and the x-axis make:

The cosine is the length of the adjacent side (which is the x-coordinate) divided by the length of the hypotenuse (which is 1). So the cosine is just the x-coordinate!

Similarly, the sine is the length of the opposite side (which is the length of the y-coordinate) divided by the length of the hypotenuse (which is 1). So the sine is the y-coordinate.

The trigonometric ratio defining the tangent (opposite over adjacent) may be less intuitive from the unit circle, but I hope you can see from the unit circle why the tangent of an angle is equal to the sine of the angle over the cosine.

answer: both chords and diameters have two endpoints on a circle. diameters must intersect the center of a circle.