Double Angle Formulas

Question 1

sin (2u)

Answer 1

2 sin (u) cos (u)

Question 2

cos (2u)

Answer 2

cos^2 (u) - sin^2 (u) 
OR 
2 cos^2 - 1
OR
1 - 2 sin^2 (u)

Question 3

tan (2u)

Answer 3

2 tan (u) / (1 - 2 tan^2 (u))