（1）mtan0°+xcos90°-psin180°-qcos270°-rsin360°=0

（2）tan20°+tan40°+

3

tan20°tan40°

=tan60°（1-tan20°tan40°）+

3

tan20°tan40°

=

3

-

3

tan20°tan40°+

3

tan20°tan40°

=

3

（3）cos

π

9

•cos

2π

9

•cos

4π

9

=

sin π 9 •cos π 9 •cos 2π 9 •cos 4π 9

sin π 9

=

1 2 sin 2π 9 •cos 2π 9 •cos 4π 9

sin π 9

=

1 4 sin 4π 9 cos 4π 9

sin π 9

=

1 8 sin 8π 9

sin π 9

=

1

8

log₂cos

π

9

+log2cos

2π

9

+log2cos

4π

9

=log₂（cos

π

9

•cos

2π

9

•cos

4π

9

）=log₂

1

8

=-3