Sine Cosine Degrees Unit Circle

We use the Unit Circle to construct the sine and the cosine functions. The unit circle is called the unit circle because:

• It is only one circle

• The area of the circle is equal to one

• Because its radius is equal to one

• Because its circumference is equal to one

cos 90°

• 0

• 1

• -1

• undefined

cos 135°

• √2/2

• -√2/2

• √3/2

• -√3/2

sin 180°

• 0

• 1

• -1

• undefined

In the unit circle, the cosine of an angle would be...

• The y-value of the point on the circle

• The x-value of the point on the circle

• y/x using the point on the circle

• None of the above

Based on the unit circle, what is the value of sin?

• y/r

• x/r

• r/y

• y/x

Answer explanation

The sin is always the y coordinate divided by the radius. With the unit circle that radius is 1.

sin π/4

• √2∕2

• 1/2

• √3/2

• 0

Based on the unit circle, what is the value of cos?

• y/r

• x/r

• r/y

• y/x

sin 0

• 1

• -1

• 0

• Undefined

sin 150

• -1/2

• -√3/2

• 1/2

• √3/2