Đáp án:
$D=−9x^2+31x−11\\ x=\dfrac{1}{3}; D=-\dfrac{5}{3}\\ E=8x−66\\ x=\dfrac{1}{5};E=-\dfrac{322}{5}\\ F=−7x^2+82x+14\\ x=-3; F=−295\\ G=−12x^2+20x−20\\ x=1; G=-12$
Giải thích các bước giải:
$D=(x-5)(-3x+1)-3(x-2)(2x-1)\\ =-3x^2+x+15x-5-3(2x^2-x-4x+2)\\ =-3x^2+16x-5-6x^2+3x+12x-6\\ =−9x^2+31x−11\\ x=\dfrac{1}{3}; D=−9.\left(\dfrac{1}{3}\right)^2+31.\dfrac{1}{3}−11=-\dfrac{5}{3}\\ E=(x-7)(x+8)-(x-5)(x-2)\\ =x^2+8x-7x-56-(x^2-2x-5x+10)\\ =x^2+x-56-x^2+2x+5x-10\\ =8x−66\\ x=\dfrac{1}{5};E=8.\dfrac{1}{5}−66=-\dfrac{322}{5}\\ F=-3(x-8)(2x+1)-(x+5)(-3x+2)-4x(x-6)\\ =-3(2x^2+x-16x-8)-(-3x^2+2x-15x+10)-4x^2+24x\\ =-6x^2-3x+48x+24+3x^2-2x+15x-10-4x^2+24x\\ =−7x^2+82x+14\\ x=-3; F=−7.(-3)^2+82.(-3)+14=−295\\ G=(5x-4)(-2x+5)-7x(x^2-4x+3)+(x^2-4x)(7x-2)\\ =-10x^2+25x+8x-20-7x^3+28x^2-21x+7x^3-2x^2-28x^2+8x\\ =−12x^2+20x−20\\ x=1; G=−12.1^2+20.1−20=-12$
