[ (x^2 + 2x -3) / (x - 4) ]
_____________________
[ (2x^2 + 5x - 3) / ( x^2 - 16) ]
[ (x + 3) (x - 1) / (x -4) ]
___________________
[ (2x - 1) ( x + 3) ] / [ (x - 4) (x + 4) ]
[ ( x + 3) ( x - 1) / (x - 4) * [ (x - 4) ( x + 4) ] / [ (2x -1) ( x + 3) ]
[ ( x + 3) ( x - 1) ( x - 4) ( x + 4) ]
__________________________
[ ( x -4) (2x - 1) ( x + 3) ]
[ (x -1) ( x + 4) ]
____________
2x - 1
x^2 + 3x - 4
___________
2x - 1