1) 3(1+2ху)(1-2ху)=3(1-4х^2y^2)=3-12x^2y^2
2)(x^2-y^3)^2=x^4-2x^2y^3+y^6
3)(a+b)^2-(a-b)^2=a^2+2ab+b^2-a^2+2ab-b^2=4ab
550000/100=5500 - 1\%