0.2x=0.8x-7.8(x=-13,x=13,x=12)

（X+X)+(X-X)+(X*X)+(X/X)=100 1x+2x+3x+4x+5x+6x+7x+8x+9x+10x+11x+12x+13x+14x+15x=550 4x+9x=13x X+13%X-28%X=3. x+13%x-28%x=3.4 若x=π/3,｜x+1|+|x+3|+...+|x+13|-|x+2|-|x+4|-...-|x+12| 求1/2x^2-1/4x+0.2x^3+0.25x-0.5x^2-1/5x^3+0.5x-1 其中x=12/13 13x-6.3x+x=46.8 x=多少 x+x=x+15 0.2x+0.4x=12 x=?20x+x=420 x=? 解方程((13x-x^2)/(x+1))(x+(13-x)/(x+1))=42 (13x-x^2)/(x+1)[x+(13-x)/(x+1)]=42