6x-x=5x,4y-5y=-y怎么算的?是不是合并同类项?

二元一次方程(x+y)/2+(x-y)/3=6,4(x+y)-5(x-y)=2怎么算 6x-x=5x,4y-5y=-y怎么算的?是不是合并同类项? 若(x*x+y*y)(x*x+y*y)-4x*x*y*y=0,求代数式(x*x+5xy+y*y)/(x*x+2xy+y*y)的值 x=3,y=4,z=5,求以下表达式的值,怎么算 (x && y)==(x || z) (x>y)+(y!=z) || (x+y)&&(y-z) x++ -y+(++z) 规定x*y=4x-5y,求6*3的值.怎么算的！ x+x+x+y+y=6.4 y+y+y+x+x=7.1 怎么算? 4x方y/(x-2y)(x+2y)怎么算[x方/x-2y]-4x方y/(x-2y)(x+2y)=? 5x-4y(y-x)=? (y-x)(x-y)^3(y-x)^5怎么算 y/(x+y)-x/(x-y)=?怎么算? 3x+2=y 5x+4=y 7x+6=y 9x+8=y 11x=y怎么解 已知5x-4y=0,求x:y和x+y:y的值 2y''+5y'=x的通解怎么算 y=(x^2-4x-5)/(x^2-3x-4)的值域是答案是y≠1且y≠6/5怎么算的? x^2+2y^2-2x+y-3=0与2x^2+5y^2-4x+y-6=0 的方程组怎么解 （x+y-5)*（x+y-5)+（x-y+3)=0 x*x-y*y y-x/7-x+y/6=1/2 5(x+y)-2(y-x)=1怎么解答 5x+4y=22 4x+y=3y+x 怎么解