sin2a - cos2a / sin2a cos 2a, если tg a = 0,5

sin2a/(1+cos2a)=1/2

2sin2a-1=sqrt(1-sin^2(2a))

sin2a=t

(2t-1)^2=1-t^2

4t^2+1-4t=1-t^2

5t^2-4t=0

5t=4

t=4/5

(tg2a-1)/sin2a=(((2*0,5)/(1-1/4)-1))*(5/4)=(4/3-1)*(5/4)=5/12