What am I doing wrong second derrivatives?

I'm trying to solve $\frac{d^2}{dx^2}(\frac{x^2}{x-5} )$ but there's one bit I keep getting wrong and I don't understand why. I keep trying to simplify the answer which is $\tfrac{(2x-10)(x-5)^2-2(x-5)(x^2-10x)}{(x-5)^4} $ but in my textbook it is telling me to factor out the common term on top of the fraction like this.

$(x-5)((2x-10)(x-5)-2(x^2-10x))=(2x-10)(x-5)-2(x^2-10x)$ 

But I don't understand how the two are equal.

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