(1)原式=(100-1)(100+1),
=1002-1,
=10000-1,
=9999;
(2)(4x2y+5xy-7y)-(5x2y-4xy+x),
=4x2y+5xy-7y-5x2y+4xy-x,
=(4-5)x2y+(5+4)xy-7y-x,
=-x2y+9xy-7y-x;
(3)(x-2y)2+4(x-y)(x+y),
=x2-4xy+4y2+4x2-4y2,
=5x2-4xy;
(4)设:a+2b=m,
则原式(a+2b-c)(a+2b+c)=(m-c)(m+c),
=m2-c2,
∵a+2b=m,
∴m2-c2=(a+2b)2-c2,
=a2+4ab+4b2-c2;
(5)(2x3y4z2+4x3y3z3-6x2y3z5)÷(2x2yz2),
=2x3y4z2÷2x2yz2+4x3y3z3÷2x2yz2-6x2y3z5÷2x2yz2,
=xy3+2xy2z-3y2z3;
(6)(x+3y)(x-2y)-x3÷x+6y2,
=x2+xy-6y2-x2+6y2,
=xy,
当x=2,y=-3时,
原式=2×(-3)=-6
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