-2x^2y+xy+13xy-(-5x^2y)
=-2x^2y+xy+13xy+5x^2y
=(-2x^2y+5x^2y)+(xy+13xy)
=3x^2y+14xy
a-(3a+b)+2（a-2b）
=a-3a-b+2a-4b
=(a-3a+2a)-(b+4b)
=0-5b
=-5b