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).