How do you evaluate `cos (-225)`?

Related questions

• How do you find the trigonometric functions of any angle?
• What is the reference angle?
• How do you use the ordered pairs on a unit circle to evaluate a trigonometric function of any angle?
• What is the reference angle for `140^\circ`?
• How do you find the value of `cot 300^@`?
• What is the value of `sin -45^@`?
• How do you find the trigonometric functions of values that are greater than `360^@`?
• How do you use the reference angles to find `sin210cos330-tan 135`?
• How do you know if `sin 30 = sin 150`?
• How do you show that `(costheta)(sectheta) = 1` if `theta=pi/4`?