1. cos (x + y) = cosx * cosy – sinx * siny

2. sin (x + y) = sinx * cosy + cosx * siny

3. sin (x – y) = sinx * cosy – cosx * siny

4. cos (x – y) = cosx * cosy + sinx * siny

5. tg (a + b) = tga + tgb/1 – tga * tgb

6. tg (a – b) = tga – tgb/1 + tga * tgb

7. ctg (a + b) = ctga – ctgb – 1/ctga + ctgb

8. ctg (a – b) = ctga * ctgb + 1/ctgb – ctga