=2sin20°+cos10°+
| sin20°sin10° |
| cos20° |
=
| 2sin20°cos20°+cos10°cos20°+sin20°cos10° |
| cos20° |
=
| sin40°+cos10° |
| cos20° |
=
| cos50°+cos10° |
| cos20° |
=
| 2cos30°•cos20° |
| cos20° |
=2cos30°
=
| 3 |
故答案为:
| 3 |
| sin20°sin10° |
| cos20° |
| 2sin20°cos20°+cos10°cos20°+sin20°cos10° |
| cos20° |
| sin40°+cos10° |
| cos20° |
| cos50°+cos10° |
| cos20° |
| 2cos30°•cos20° |
| cos20° |
| 3 |
| 3 |