已知在数轴上一个点到原点的距离是2，则这个点表示的数是______．

已知22x+1+4x=48，求x的值．

计算：-（y3）2=______；（a2n）3=______；[（2a-b）3]2=______．

--------Oh,your country is not what it use to be when I visited it twenty years ago..-------Yes. Great changes, especially in the eastern areas,________since then.
A. took placeB. have been takenplaceC. have taken placeD. has been taken place

列代数式：（1）a的4倍与b的差；（2）被7除商是x，余数是4的数．

合并同类项后，所得项的系数是合并前（）的和，且（）不变。