Question

Evaluate without using trignometric table

Answer 1

tan(2a)=cot(a-21) where 2a is a Acute angle
cot(90-2a) = cot(a-21)
90-2a = a-21
-2a-a = -21-90
-3a = -111
3a=111
a = 111/3
a=37
a is an acute angle because it's less than 90 degree angle