| sinα•(−cosα)•tanα |
| −cosα•sinα•sinα |
=
| tanα |
| sinα |
| 1 |
| cosα |
（Ⅱ）当n=2k，k∈Z时原式=
| sin(2kπ+α) |
| cos(2kπ−α) |
| sinα |
| cosα |
当n=2k+1，k∈Z时原式=
| sin(2kπ+π+α) |
| cos(2kπ+π−α) |
| −sinα |
| −cosα |
∴当n∈Z时原式=tanα
| sin(α−2π)cos(α+π)tan(α−99π) |
| cos(π−α)sin(3π−α)sin(−α−π) |
| sin(nπ+α) |
| cos(nπ−α) |
| sinα•(−cosα)•tanα |
| −cosα•sinα•sinα |
| tanα |
| sinα |
| 1 |
| cosα |
| sin(2kπ+α) |
| cos(2kπ−α) |
| sinα |
| cosα |
| sin(2kπ+π+α) |
| cos(2kπ+π−α) |
| −sinα |
| −cosα |