前面我们已经学过2+2+2+2=2×4,而2+2+...+2n个比较长,可以记为2n.如果换成n个2相乘,即2+2+...+2n,又该怎么记呢?我们在小学的时候学过正方形的面积和正方体的体积.如果一个正方形的边长为a,则它的面积应为a·a,也可表示为____;如果一个正方体的棱长为a,那么它的体积应为a·a·a,也可表示为____.由此我们能得到什么启示呢?更一般地,如果n个相同的因数a相乘, We have learned in the past that 2+2+2+2=2×4, and 2+2+...+2n are longer, which can be written as 2n. If we replace n with 2 multiplication, that is 2+2+ ... +2n, how should we remember? We learned the area of ​​the square and the volume of the cube in elementary school. If a square has a side length of a, its area should be a·a, it can also be expressed as ____; If a cube has a length of a, then its volume should be a·a·a, or it can be expressed as ____. So what can we learn from it? More generally, if there are n same factors a multiply,