3.3 – The Unit Circle and Circular Functions Math 150 3.3 – The Unit Circle and Circular Functions

Recall: We’ve defined the sine function in two ways: sin 𝜃 = 𝑦 𝑟 and sin 𝜃 = opposite hypotenuse .

All the trig functions can also be defined in terms of the unit circle (circle with radius 1, centered at the origin). Since 𝑠=𝜃𝑟, notice that on the unit circle 𝑠=𝜃. So, angles and arc lengths on the unit circle are the same.

All the trig functions can also be defined in terms of the unit circle (circle with radius 1, centered at the origin). Since 𝑠=𝜃𝑟, notice that on the unit circle 𝑠=𝜃. So, angles and arc lengths on the unit circle are the same.

All the trig functions can also be defined in terms of the unit circle (circle with radius 1, centered at the origin). Since 𝑠=𝜃𝑟, notice that on the unit circle 𝑠=𝜃. So, angles and arc lengths on the unit circle are the same.

So, the trig functions we learned about in 1 So, the trig functions we learned about in 1.3 become: 𝐬𝐢𝐧 𝒔 =𝒚 𝐜𝐬𝐜 𝒔 = 𝟏 𝒚 𝐜𝐨𝐬 𝒔 =𝒙 𝐬𝐞𝐜 𝒔 = 𝟏 𝒙 𝐭𝐚𝐧 𝒔 = 𝒚 𝒙 𝐜𝐨𝐭 𝒔 = 𝒙 𝒚 In particular, note that on the unit circle, 𝑥 is cosine and 𝑦 is sine.

So, the trig functions we learned about in 1 So, the trig functions we learned about in 1.3 become: 𝐬𝐢𝐧 𝒔 =𝒚 𝐜𝐬𝐜 𝒔 = 𝟏 𝒚 𝐜𝐨𝐬 𝒔 =𝒙 𝐬𝐞𝐜 𝒔 = 𝟏 𝒙 𝐭𝐚𝐧 𝒔 = 𝒚 𝒙 𝐜𝐨𝐭 𝒔 = 𝒙 𝒚 In particular, note that on the unit circle, 𝑥 is cosine and 𝑦 is sine.

Side note: the trig functions are sometimes called the circular functions.

Instead of reference angles (from 2 Instead of reference angles (from 2.2), we use reference numbers (also called reference arcs). Reference numbers are the shortest distance along the unit circle to the 𝑥-axis.

Ex 1. Find the exact values of the following Ex 1. Find the exact values of the following. sin 3𝜋 2 cos 3𝜋 2 tan 3𝜋 2

Ex 1. (continued) cos 4𝜋 3 sin 4𝜋 3 tan − 9𝜋 4

Ex 1. (continued) cos 4𝜋 3 sin 4𝜋 3 tan − 9𝜋 4