化简: .
3a2b2c÷(-a2b2)=________;
a2bx3÷a2x=_________;
填空:(1)1010÷______=109; (2)a8÷a4=_____;(3)(-b)9÷(-b)7=________;(4)x7÷_______=1;(5)(y5)4÷y10=_______;(6)(-xy)10÷(-xy)5=_________.
若3n=27,则21-n=______.
当x______时,(3x+2)0=1有意义,若代数式(2x+1)-4无意义,则x=________.