(5x^3-3x^2+7x-2)(3x^2+2x-3)
x^3项有5x^3*(-3)+(-3x^2)*2x+7x*3x^2
=-15x^3-6x^3+21x^3
=0
x^2项有(-3x^2)*(-3)+7x*2x+(-2)*3x^2
=9x^2+14x^2-6x^2
=17x^2
所以x^3的系数是0,x^2系数是17
(ax^3-x+6)(3x^2+5x+b)
=3ax^5+5ax^4+(ab-3)x^3+13x^2+(30-b)x+6b
=6x^5+10x^4-7x^3+13x^2+32x-12
所以3a=6
5a=10
ab-3=-7
30-b=32
6b=-12
所以a=2,b=-2