Question 85799
5 / (x^2 - 16) -  3 / (x^2 - x - 12)

= 5 /[(x-4)(x+4)] - 3/[(x-4)(x+3)]

least common denominator is (x-4)(x+4)(x+3)

= 5(x+3)/lcm - 3(x+4)/lcm

= [5x+15-3x-12]/lcm

= [2x+3]/lcm

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Cheers,
Stan H.