=(2x+1)^2-(x+3)^2-[(x-1)^2-1]
=(2x+1+x+3)*(2x+1-x-3)-(x-1+1)*(x-1-1)
=(x-2)*(3x+4-1)
=2*(x+2)*(x-2)
=2x^2-8怎么不是按照多项式乘多项式的法则来做的？是的啊，相乘展开后化简