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Home > INT3 > Chapter 12 > Lesson 12.2.3 > Problem 12-110

12-110.

Show how to derive the double angle formulas for sin(2x) and cos(2x) by substituting x for both α and β in the formulas for sin(α + β) and cos(α + β), then simplifying. Homework Help ✎

sin(x + x)

What is this equivalent to? How can you change it?

sin(x + x) = sin(x)cos(x) + cos(x)sin(x) = 2sin(x)cos(x)

Now use the same method to find the the double angle formula for cos(2x).