Exercise #18 Double Angle Identities

2 2

sin 2 2sin cos

cos 2 cos sin

2

2

2cos 1

1 2sin

2

2 tantan 2

1 tan

Example Evaluate cos120 using the double angle formula. Example

If 4

sin5

and 3

cos5

, find tan 2 .

OR

OR

Example

Solve sin 2 sin over the interval 0,2 .

Example

Given that cos 0.9920

, evaluate cos

10

.

Try

Evaluate cos7

given that cos 0.9714

.