(x²+x+6)(x²-x+6)
=(x²+6+x)(x²+6-x)
=(x²+6)²-x²
=x^4+12x²+36-x²
=x^4+11x²+36
(-5x+2y)²
=25x²-20xy+4y²
（-3m-4n）²
=9m²+24mn+16n²
（x+1）²-2x+1
=x²+2x+1-2x+1
=x²+2