Trig identies

Question 1

cos(2θ)

Answer 1

cos²(θ)-sin²(θ)
2cos²(θ)-1
1-2sin²θ

Question 2

sin2θ

Answer 2

2sin(θ)cos(θ)

Question 3

tan(2θ)

Answer 3

2tan(θ)/1-tan²(θ)

Question 4

Pythagorean identities

Answer 4

sin²(θ)+cos²(θ)=1
tan²(θ)+1=sec²(θ)
1+cot²(θ)=csc²(θ)

Question 5

cos(a+b)

Answer 5

cos(a)cos(b)-sin(a)sin(b)

Question 6

sin(a+b)

Answer 6

sin(a)cos(b)+cos(a)sin(b)