~ Bạn tham khảo ~
`a, 4/[x+2]+2/[x-2]+[5x-6]/[4-x^2]`
`= [4(x-2)]/[(x+2)(x-2)] + [2(x+2)]/[(x-2)(x+2)] - [5x-6]/[(x+2)(x-2)]`
`= [4x-8+2x+4-5x+6]/[(x-2)(x+2)]`
`= [x+2]/[(x-2)(x+2)]`
`= 1/[x-2]`
`b, [1-3x]/[2x]+[3x-2]/[2x-1]+[3x-2]/[2x-4x^2]`
`= [(2x-1)(1-3x)]/[2x(2x-1)]+[2x(3x-2)]/[2x(2x-1)]-[3x-2]/[2x(2x-1)]`
`= [-6x^2+5x-1+6x^2-4x-3x+2]/[2x(2x-1)]`
`= [-2x+1]/[2x(2x-1)]`
`= -1/[2x]`
`c,1/[x^2+6x+9]+1/[6x-x^2-9]+x/[x^2-9]`
`= [(x-3)^2]/[(x-3)^2(x+3)^2]-[(x+3)^2]/[(x-3)^2(x+3)^2]+[x(x-3)(x+3)]/[(x-3)^2(x+3)^2]`
`= [x^2-6x+9-x^2-6x-9+x^3-9x]/[(x-3)^2(x+3)^2]`
`= [x^2-21x]/[(x-3)^2(x+3)^2]`
`= [x(x^2-21)]/[(x-3)^2(x+3)^2]`
