- #1

- 160

- 0

## Homework Statement

I have to prove that sin^2(a/2) = (1-cosa)/(2)

cosa = cos(2*(a/2)) = 1 -2sin^2(a/2)

I dont understand this step that was given in the solutions how do I get it?

- Thread starter needingtoknow
- Start date

- #1

- 160

- 0

I have to prove that sin^2(a/2) = (1-cosa)/(2)

cosa = cos(2*(a/2)) = 1 -2sin^2(a/2)

I dont understand this step that was given in the solutions how do I get it?

- #2

- 116

- 2

- #3

- 160

- 0

- #4

- 116

- 2

Now assuming b=a/2, you have cos(2b)=cos^2(b)-sin^2(b) indeed... now you can use the fundamental formula cos^2(b)+sin^2(b)=1 and express cos(2b) only as function of the sin^2(b). Done this, all is straightforward replacing b with a/2

- Last Post

- Replies
- 10

- Views
- 1K

- Last Post

- Replies
- 2

- Views
- 916

- Last Post

- Replies
- 5

- Views
- 1K

- Last Post

- Replies
- 4

- Views
- 1K

- Replies
- 8

- Views
- 3K

- Replies
- 7

- Views
- 1K

- Replies
- 4

- Views
- 1K

- Replies
- 3

- Views
- 2K

- Replies
- 3

- Views
- 2K

- Replies
- 2

- Views
- 2K