### Home > A2C > Chapter 13 > Lesson 13.2.3 > Problem13-131

13-131.

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

cos(x + x) = cos(x)cos(x) − sin(x)sin(x) = cos2(x) − sin2(x)