Sine and Cosine 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

sin 210°

cos 90°

• 0

• 1

• -1

• undefined

cos 135°

• √2/2

• -√2/2

• √3/2

• -√3/2

sin 180°

• 0

• 1

• -1

• undefined

cos 180°

• 0

• 1

• -1

• undefined

sin 150°

• 1/2

• -1/2

• √3/2

• -√3/2

cos(60°)

• 0
• 1/2
• √3/2
• 1

cos 300^o

• -1/2

• 1/2

• √3/2

• -√3/2

What is the radius of a unit circle?

• 1
• 2
• 1/2
• 0