(sin2a/sina)-(cos2a/cosa)=(sin2a*cosa-cos2a*sina)/(sina*cosa)=
=sin(2a-a)/(sina*cosa)=sina/(sina*cosa)=1/cosa
(1/sinx-cosx/sinx)(1/sinx+cosx/sinx)-1=(1-cos^2x)/sin^2x-1=sin^2x/sin^2x-1=1-1=0
X *5= 4*8
5x=32
x=32:5
x=6.4
X²+20x+91=x²+13x+7x+91=x*(x+13)+7(x+13)=(x+7)*(x+13)