1.原式=x²+6x+x+6=x²+7x+6
2.原式=36x四次方+(-27)·x=36x四次方-27x
3.原式=x²-4xy+4y²-(x²-4y²)-(4x²-2xy)
=-4xy+8y²-4x²+2xy
=-4x²-2xy+8y²