# How do you find the exact values of #costheta# and #sintheta# when #tantheta=1#?

##### 2 Answers

OR

#### Explanation:

Given:

Use the identity:

Substitute

Because

Because we are given nothing to determine whether

OR

#### Explanation:

Draw a right isosceles triangle. The angles are 45, 45,90

Tan 45 =1,

Using Pythagoras the sides are in the ratio

cos 45=sin45=

But then we need to look at the angle in the third quadrant to get the negative result.