`c)[x+5]/[2x-4].[4-2x]/[x+2]` `ĐK: x \ne -2;x \ne 2`
`=[-(x+5)]/[x+2]=[-x-5]/[x+2]`
____________________________________________________
`d)8/[x^2+2x-3]+2/[x+3]+1/[x-1]` `ĐK: x \ne -3;x \ne 1`
`=[8+2(x-1)+x+3]/[(x-1)(x+3)]`
`=[8+2x-2+x+3]/[(x-1)(x+3)]`
`=[3x+9]/[(x-1)(x+3)]=3/[x-1]`
____________________________________________________
`e)[1-4x^2]/[x^2+4x].[3x]/[2-4x]` `ĐK: x \ne 0,x \ne -4,x \ne 1/2`
`=[(1-2x)(1+2x).3x]/[x(x+4).2(1-2x)]`
`=[3(1+2x)]/[2(x+4)]`
`=[3+6x]/[2x+8]`
____________________________________________________
`f)(9/[x^3-9x]+1/[x+3]):([x-3]/[x^2+3x]-x/[3x+9])`
`=[9+x(x-3)]/[x(x-3)(x+3)]:[3(x-3)-x^2]/[3x(x+3)]`
`=[9+x^2-3x]/[x(x-3)(x+3)].[3x(x+3)]/[3x-9-x^2]`
`=[-3]/[x-3]`
