x(x+y)-(x-y)(x+y)-y^2,当x=4^-2007,y=-4^2008.

题目

x(x+y)-(x-y)(x+y)-y^2,当x=4^-2007,y=-4^2008.
我只想校对一下.
急!
我化出来原式=xy.然后结果怎么算!

答案

x(x+y)-(x-y)(x+y)-y^2
=x²+xy-x²+y²-y²
=xy
=4^(-2007)*(-4^2008)
=-4^(-2007)*4^2007*4
=-4^(-2007+2007)*4
=-4^0*4
=-4