计算:2a2b+5ab-(-a2b+3ab)
解:2a2b+5ab-(-a2b+3ab)
=2a2b+5ab+a2b-3ab…①
=2a2b+a2b+5ab-3ab…②
=(2a2b+a2b)+(5ab-3ab)…③
=3a2b+2ab…④
解:(-6)+(-15)+(+6)
=(-6)+(+6)+(-15)()
=[(-6)+(+6)]+(-15)()
=0+(-15)()
=-15()