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More Lessons for High School Regents Exam
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High School Math based on the topics required for the Regents Exam conducted by NYSED.

What are Cofunctions?
Cofunctions are pairs of trigonometric functions that have equal values when their arguments are complementary angles.
Sine and Cosine are cofunctions because sin θ = cos (90° - θ)
Secant and Cosecant are cofunctions because sec θ = csc 90° - θ)
Tangent and Cotangent are cofunctions because tan θ = cot 90° - θ)

What are Cofunction Identities?
A function f is cofunction of a function g if f(A) = g(B) when A and B are complementary angles.
sin(A) = cos(B), if A + B = 90°
sec(A) = scs(B), if A + B = 90°
tan(A) = cot(B), if A + B = 90°

The following figures give the cofunction identities. Scroll down the page for more examples and solutions.

Cofunction Identities

What is a cofunction?
Finding the cofunction.
Using the cofunction relationship
Cofunction Identities
This video explains the cofunction identities and how to determine cofunctions given a function value. Most cofunction values are verified on a calculator.
Cofunction Identities - Solving Trigonometric Equations
This video explains how to use cofunction identities to solve trigonometric equations.

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