| cos27,5 − sin27,5 | sin267,5 − cos267,5 | ||
+ | = | ||
| cos7,5sin7,5 | cos67,5sin67,5 |
| 2cos(15) | 2cos(135) | ||
− | = 2ctg(15) − 2ctg(135) = 2(ctg(15) − ctg(135)) | ||
| sin(15) | sin(135) |
| ctg(45) * ctg(30) + 1 | √3 + 1 | |||
ctg(15) = ctg(45 − 30) = | = | = | ||
| ctg(30) − ctg(45) | √3 − 1 |
| (√3 + 1)2 | 4 + 2√3 | |||
= | = | = 2 + √3 | ||
| 3 − 1 | 2 |