x的m次方乘以x的n次幂的3次方除以（x的m-1次方乘以2x的n-1次方）等于多少啊?

(x^m)*(x^n)³÷[x^(m-1)*2x^(n-1)]
=x^(m+3n)÷2x^(m+n-2)
=(1/2)x^[(m+3n)-(m+n-2)]
=(1/2)x^(2n+2) ----------即1/2倍的“x的(2n+2)次方”.还有一个问题，x的2n次方+x的2n次方-x的n+2次方x^2n+x^2n-x^(n+2)=2x^2n-x^(n+2).(这就是最终结果了,要清楚:只有同类项才能合并!)