Respuesta :

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

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