Bài 2:
a: \(\left(a+b\right)^3-3ab\left(a+b\right)\)
\(=a^3+b^3+3a^2b+3ab^2-3ab^2-3a^2b\)
\(=a^3+b^3\)
b: \(\left(a-b\right)^3+3ab\left(a-b\right)\)
\(=a^3-3a^2b+3ab^2-b^3+3a^2b-3ab^2\)
\(=a^3-b^3\)
Bài 1:
a: \(\left(3-2x\right)^2=3^2-2\cdot3\cdot2x+\left(2x\right)^2=9-12x+4x^2\)
b: \(\left(xy+5\right)^2=\left(xy\right)^2+2\cdot xy\cdot5+5^2=x^2y^2+10xy+25\)
c: \(\left(2x+1\right)\left(1-2x\right)=1-4x^2\)
d: \(\left(1-5x\right)^3=1^3-3\cdot1^2\cdot5x+3\cdot1\cdot\left(5x\right)^2-\left(5x\right)^3\)
\(=1-15x+75x^2-125x^3\)
e: \(\left(2x+y\right)\left(4x^2-4xy+y^2\right)\)
\(=\left(2x+y\right)\left(2x-y\right)^2\)
\(=\left(4x^2-y^2\right)\left(2x-y\right)=8x^3-4x^2y-2xy^2+y^3\)
