答：
x²-5x=3
(x-1)(2x-1)-x(x+3)+15/(x²-3)
=2x²-3x+1-x²-3x+15/(5x)
=x²-5x-x+1+3/x
=3-x+1+3/x
=4-x+3/x
=4+(3-x²)/x
=4+(-5x)/x
=4-5
=-1