Trig Identities Flashcards
1
Q
sin(-θ) =
A
-sinθ
2
Q
cos(-θ) =
A
cosθ
3
Q
sin(x + y) =
A
sin(x)cos(y) + cos(x)sin(y)
4
Q
cos(x + y) =
A
cos(x)cos(y) - sin(x)sin(y)
5
Q
cos(x - y) =
A
cos(x)cos(y) + sin(x)sin(y)
6
Q
sin2x =
A
2sin(x)cos(x)
7
Q
cos2x =
hint:* can be three answers!
A
= cos²x - sin²x
…and by 1 = cos²x + sin²x
= 2cos²x - 1
= 1 - 2sin²x
8
Q
cos²x =
A
= [1 + cos²x] / 2
9
Q
sin²x =
A
= [1 - cos²x] / 2
10
Q
sinxcosx =
A
1/2 * [sin(x + y) + sin(x - y)]
11
Q
cosxcosy =
A
1/2 * [cos(x + y) + cos(x - y)]
12
Q
sinxsiny
A
1/2 * [cos(x + y) - cos(x - y)]
13
Q
sin²θ + cos²θ
A
= 1
