for f(x)= (-1/x^2)
[ x^2 - a^2 ]/ [x^2 a^2 (x-a)] [(x+a)(x-a)] / [x^2 a^2 (x-a)] (x+a)/x^2a^2 note for when you get to differentiation the limit of this as x-->a is 2x/x^4 = 2/x^3
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