-5a-（4a+3b）+(a-2b)
=-5a-4a-3b+a-2b
=(-5-4+1)a-(3+2)b
=-8a-5b
3(a^2-ab)-5（ab+2a^-1）
=3a^2-3ab-5ab-10a^2+5
=(3-10)a^2-(3+5)ab+5
=-7a^2-8ab+5