(2x+3y)2﹣2(2x+3y)(2x﹣3y)+(2x﹣3y)2,其中x= 12 ,y= 13 .
I don't think looking after(照看)children is just work.
设集合M={x|x=k2+12,k∈Z},N={x|x=k4+12,k∈Z}则( )