(0.75a^4b^3c-½a^4b^5-1/10a^3b^2)÷ (-0.5a^3b^2)=-1.5abc+ab^3+0.1若x^2+mx-15=(x+3)(x+n),则mn的值为3n=-15 m=3+nm=-2 n=-5已知ab=9,a-b=-3,则a^2+3ab+b^2=(a-b)^2+5ab=9+45=54