Here is some thoughts on this:
cos 57 = sin (90-57) = sin 33
so cos 57 . cosec 33 = cos 57 / sin 33 = sin 33 / sin33 = 1
2 cos 60 = 2 * 1/2 = 1
so the last 2 parts work out to 0
now we have to find cos 70 / sin 20
sin 20 = cos 70 so this comes to 1
so finally the answer is 1
