Trigonometric Identities and Equations
Section 7‐3
Sum and Difference Identities
Finding the exact value of a trigonometric functions
• You can use the sum and difference identities and the values of the special trigonometric functions (like 45degrees, 30 degrees and 60 degrees) to find the values of trigonometric functions of other angles.
Common Mistake!
• The distributive property does not hold for the trigonometric functions.
• In other words, for example:
Sin ( x + y ) ≠ Sin x + Sin y
Why do I need to use the difference identity to calculate the value of a trigonometric function when I can use my calculator!
The calculator gives you a decimal approximation. In some real life applications, you need the EXACT value. This is when the sum and difference identities come in use.
HW # 3
• Section 7‐3
• Pp. 442‐445
• #15‐35 odd, 43, 51, 55