①（3x+2y-4）²
=9x^2+6xy-12x+6xy+4y^2-8y-12x-8y+16
=9x^2+12xy-24x+4y^2-16y+16
②(a-2b+3c)(a+2b-3c)
=a^2+2ab-3ac-2ab-4b^2+6bc-3ac+6bc-9c^2
=a^2-4b^2-9c^2-6ac+12bc