Hi there!
~
cosec 20 -cot 40= 1/sin 20 - cos 40/sin 40
= (sin 40 -cos 40 sin20)/(sin 40 sin 20)
= 1/sin 40 ( 2 cos 20 - cos 40)
=1/sin20 ( 2 cos(60-40)-cos 40)
=1/sin40( 2 cos 60 cos 40 - 2 sin 60 -sin 40-cos 40)
Put the value of cos 60
= 1/sin 40 ( 2 sin 60 sin 40)
=root(3)
Hope this helped you!