30 tháng 7 2023 lúc 18:45
1: (4a-b)(4a+b)=(4a)^2-b^2=16a^2-b^2
(x^2y+2y)(x^2y-2y)
=(x^2y)^2-4y^2
=x^4y^2-4y^2
(3/4x+3/5y)(3/5y-3/4x)=(3/5y)^2-(3/4x)^2=9/25y^2-9/16x^2
2: (x+2)(x^2-2x+4)=x^3+8
(3x+2y)(9x^2-6xy+4y^2)=27x^3+8y^3
3: (5-3x)(5+3x+9x^2)=125-27x^3
(1/2x-1/5y)(1/4x^2+1/10xy+1/25y^2)=1/8x^3-1/125y^3
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