| π |
| 4 |
| 3 |
| 5 |
∴
| sin2x−2sin2x |
| 1−tanx |
=
| 2sinx(cosx−sinx) | ||
1−
|
=
| 2sinx(cosx−sinx)cosx |
| cosx−sinx |
=sin2x
=-cos（
| π |
| 2 |
=1-2cos2(
| π |
| 4 |
=1-2×
| 9 |
| 25 |
=
| 7 |
| 25 |
故选：A．
| π |
| 4 |
| 3 |
| 5 |
| sin2x−2sin2x |
| 1−tanx |
| 7 |
| 25 |
| 12 |
| 25 |
| 13 |
| 25 |
| 18 |
| 25 |
| π |
| 4 |
| 3 |
| 5 |
| sin2x−2sin2x |
| 1−tanx |
| 2sinx(cosx−sinx) | ||
1−
|
| 2sinx(cosx−sinx)cosx |
| cosx−sinx |
| π |
| 2 |
| π |
| 4 |
| 9 |
| 25 |
| 7 |
| 25 |