Question

$frac{1+ctg2 alpha }{1-ctg2 alpha } = frac{sin(2 alpha- frac{pi }{4} ) }{sin(2 alpha- frac{pi }{4} ) }$

Answer 1

(1+ctg2a)  / (1 -ctg2a) = sin (2a -п/4) /sin (2a -п/4) = 1
(1+ctg2a)  = (1 -ctg2a) 
2*(ctg2a) = 0 
ctg2a = 0 
2a = п/2 + пk  , k Є Z
a = п/4 + пk/2  , k Є Z
ОТВЕТ a = п/4 + пk/2  , k Є Z