**CoFunctions**

Such examinations, lead us to three sets of “cofunction” identities:

Also written:

Notice the connection of the letters C & O:

* sine and cosine cofunctions

* tangent and cotangent cofunctions

* secant and cosecant cofunctions

* complementary

**Examples**:

**1**. Find a Value of θ for which sin θ = cos 15º is true

Solution: Since sine and cosine are cofunctions, we know that the value will be the complement of 15º.

Answer: 75º

**2.** Write the expression tan 265º as the function of an acute angle of measure less than 45º. Solution: The 265º angle is in the third quadrant with a reference angle of 85º. So we could write:

tan 265º = tan 85º. But the question wants an angle less than 45º, so we use our cofunctions.

tan 85º = cot 5º.

Answer: cot 5º