（-2x^2+3x+2)-3(7x^2-5x-1)-(4x^2-x+6)
=-2x^2+3x+2-21x^2+15x+3-4x^2+x-6
=-2x^2-21x^2-4x^2+3x+15x+x+2+3-6
=-27x^2+19x-1