SINE AND COSINE AS COMPLEMENTS ~ adapted from Walch Education

 Examine HEY! DOES THIS RELATIONSHIP WORK FOR sin B AND cos A?

 In, sin A = cos B, and sin B = cos A  This relationship between sine and cosine is known as an identity Using this triangle, show that this relationship works for every right triangle

WHAT ELSE?!? The two acute angles in a right triangle have a sum of 90°. They are complementary angles. WWhat is the mathematical expression?

COFUNCTION IDENTITIES This looks like something I should remember

OH…THAT’S WHAT THAT MEANS The value of one ratio for one angle is the same as the value of the other ratio for the other angle.  So we can use the sine of one acute angle to find the cosine of its complementary angle (AND VICE –VERSA)

 Let’s try this example:  Find

 First step:  Second step:  Third step: Verify using a scientific calculator.  GREAT JOB

 See if you can figure this one out. Be ready to explain which identity you used and why:  Find a value of  for which sin  = cos 15° is true.

THANKS FOR WATCHING!!!!  Ms. Dambreville