Question

1. The photo was taken from an unusual angle.

2. The photo was taken at an unusual angle.
(Which preposition do we have to use? Are both OK?)

3. Bend your knees and bend your body at 45 degree angle.

4. Bend your knees and bend your body from 45 degree angle.
(Which preposition do we have to use? Are both OK?)

Answer 1

1 and 2 -- both are OK.

3 and 4 -- both need "... a 45-degree angle."
The prepositions are OK.

http://grammar.ccc.commnet.edu/grammar/marks/hyphen.htm
Scroll down a bit and read Hyphens have other uses section. The hyphen I used above fits the "a" use.