Bài 1 : Khai triển .
a, \(\left(2x-y\right)^3=8x^3-12x^2y+6xy^2-y^3\)
b, \(27x^3+1=\left(3x+1\right)\left(9x^2-3x+1\right)\)
c, \(\left(2x\right)^3-125=\left(2x-5\right)\left(4x^2+10x+25\right)\)
Bài 2 :
a, \(x^2+10x+25=\left(x+5\right)^2=\left(x+5\right)\left(x+5\right)\)
b, \(16x^2-\left(x^2+4\right)^2=\left(4x-x^2+4\right)\left(4x+x^2+4\right)\)
c, \(x^2+3x^2+3x+1=4x^2+3x+1\)
\(=\left(2x\right)^2+\frac{2x.3}{2}+\frac{9}{4}-\frac{5}{4}=\left(2x+\frac{3}{2}\right)^2-\left(\sqrt{\frac{5}{4}}\right)^2\)
\(=\left(2x+\frac{3}{2}-\sqrt{\frac{5}{4}}\right)\left(2x+\frac{3}{2}+\sqrt{\frac{5}{4}}\right)\)
