y/5x*15x²/y=3x x/2a²b除以（-2xb）=x/2a^2b*(-1/(2xb)=-1/(4a^2b^2)1/(x-1)+1/(1+x)=(1+x+x-1)/(x-1)(x+1)=2x/(x-1)(x+1)ab/c-bc/a=(a^2b-bc^2)/(ac)=b(a+c)(a-c)/(ac)a²-1分之a+a²-1分之1=(a+1)/(a^2-1)=(a+1)/(a+1)(a-1)=1/(a-1)
