4cos50°-tan40°=4sin40°-tan40°
=

4sin40°cos40°−sin40°

cos40°

=

2sin80°−sin(30°+10°)

cos40°

=

2cos10°− 1 2 cos10°− 3 2 sin10°

cos40°

=

3 2 cos10°− 3 2 sin10°

cos40°

=

3

cos(30°+10°)

cos40°

=

3

．
故答案为：

3

．