分式 计算题第一题2x²/3y²×5y/6x÷10y/21x²第二题a+b/ab+b-c/

第一题2x²/3y²×5y/6x÷10y/21x²=2x²/3y²×5y/6x×21x²/10y=x/y×1/6×7x²/y=7x^3 /(6y^2)第二题(a+b)/(ab)+(b-c)/(bc)+(c-a)/(ac)=1/b+1/a + 1/c-1/b + 1/a-1/c=1/a + 1/a=2/a第三题1-(x-y)/(x+2y)÷(x²-y²)/(x²+4xy+4y²)= 1-(x-y)/(x+2y) × (x²+4xy+4y²)/(x²-y²)= 1-(x-y)/(x+2y) × (x+2y)²/{(x+y)(x-y)}= 1- (x+2y)/(x+y)= (x+y-x-2y)/(x+y)= -y/(x+y)第四题{ (x-2)/(x+2)-(x+2)/(x-2) } × (x²-4)/x²= { (x-2)/(x+2) -(x+2)/(x-2) } × (x+2)(x-2) /x²= { (x-2)/(x+2) × (x+2)(x-2) -(x+2)/(x-2)× (x+2)(x-2) } /x²= { (x-2)^2 -(x+2)^2 } /x²= -4x /x²= -4/x