tan40*tan50*tan60-[(cos40)^2+(cos50)^2+(cos60)^2]+sin50/4cos40
=tan40*cot40*tan60-[(sin50)^2+(cos50)^2+(cos60)^2]+sin50/4cos40
=tan60-[1+(cos60)^2]+cos40/4cos40
=√3-[1+1/4]+1/4
=√3-1-1/4+1/4
=√3-1
tan40*tan50*tan60-[(cos40)^2+(cos50)^2+(cos60)^2]+sin50/4cos40
=tan40*cot40*tan60-[(sin50)^2+(cos50)^2+(cos60)^2]+sin50/4cos40
=tan60-[1+(cos60)^2]+cos40/4cos40
=√3-[1+1/4]+1/4
=√3-1-1/4+1/4
=√3-1