3x^2-[5x-（2/1x-3）+2x^2]=

3x²；-[5x-（1/2x-3）+2x²；]
=3x²；-[5x-1/2 x+3+2x²；]
=3x²；-（2x²；+9/2 x+3）
=3x²；-2x²；-9/2 x-3
=x²；-9/2x-3