Hello Vikas dear, cos 75 = cos (90-15) = sin 15
Same way sin 75 = sin (90 - 15) = cos 15
There by the numerator becomes sin^2 15 + cos^2 15. This equals to 1
Now denominator:
tan 85 = tan (90 - 5) = cot 5
So tan 5 * tan 85 = tan 5 * cot 5 = 1
Same way tan 55 = tan (90-35) = cot 35
So tan 35 * tan 55 = tan 35 * cot 35 = 1
Moreover tan 30 = 1/./3
Plug all these we get 1 / (1/./3) = ./3
