a) Ta có: \(x^2+8x+16\)
\(=x^2+2\cdot x\cdot4+4^2\)
\(=\left(x+4\right)^2\)
b) Sửa đề: \(\left(a+b\right)^2-4^2\)
Ta có: \(\left(a+b\right)^2-4^2\)
\(=\left(a+b-4\right)\left(a+b+4\right)\)
c) Ta có: \(x^3+6x^2+12x+8\)
\(=x^3+3\cdot x^2\cdot2+3\cdot x\cdot2^2+2^3\)
\(=\left(x+2\right)^3\)
d) Sửa đề: \(9x^2-30x+25\)
Ta có: \(9x^2-30x+25\)
\(=\left(3x\right)^2-2\cdot3x\cdot5+5^2\)
\(=\left(3x-5\right)^2\)
e) Ta có: \(\frac{1}{8}x^3-8\)
\(=\left(\frac{1}{2}x\right)^3-2^3\)
\(=\left(\frac{1}{2}x-2\right)\left(\frac{1}{4}x^2+x+4\right)\)
g) Ta có: \(8x^3+27y^3\)
\(=\left(2x\right)^3+\left(3y\right)^3\)
\(=\left(2x+3y\right)\left(4x^2-6xy+9y^2\right)\)
h) Ta có: \(27-27m+9m^2-m^3\)
\(=3^3-3\cdot3^2\cdot m+3\cdot3\cdot m^2-m^3\)
\(=\left(3-m\right)^3\)
