Trig Identities

Question 1

Pythag 1 (sin and cos)

Answer 1

Sin^2 + Cos^2 = 1

Question 2

Pythag 2 (tan and sec)

Answer 2

1 + Tan^2 = Sec^2

Question 3

Pythag 3 (cot and cosec)

Answer 3

1 + Cot^2 = cosec^2

Question 4

sin double angle

Answer 4

2sinXcosX

Question 5

Cosine Double angle

Answer 5

Cos^2 - sin^2

Can then use Sin^2 + Cos^2 = 1 to rewrite

Question 6

Sin addition

Answer 6

SIN(A ± B) = sinAcosB ± cosAsinB

Question 7

cos addition

Answer 7

cos(A±B) = cosAcosB ±(opposite sign to cos(A±B) sinAsinB

Question 8

tan addition

Answer 8

tan(A±B) = (TanA ± tanB) / (1 (inv±) tanA tanB)

Question 9

sin small angle

Answer 9

sin x = x

Question 10

cos small angle

Answer 10

cos x = 1 - (x^2)/2 = 1

Question 11

tan small angle

Answer 11

tan(x) = x