Given Tan (45 + a) = 3, find the value of sin2a-2cos ^ a
tg(45+a)=(tg45+tga)/(1-tg45*tga)=(1+tga)/(1-tga)=3
So TGA = 1 / 2
sin2a-2cos^2a=sin2a-cos2a-1=2tga/(1+(tga)^2)-(1-(tga)^2)/(1+(tga)^2)-1=-4/5
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