Question

a)Thu gọn biểu thức A=( 5x-3)^2-2(5x+3)( x+3) +(x+3)^2

b) Phân tích đa thức thành nhân tử x^3 +5x^2 +6x

c) Tìm x cho biết :x^3 -3x^2 -4x +12=0

Answer 1

Answer 2

a) \(A=\left(5x-3\right)^2-2\left(5x-3\right)\left(x+3\right)+\left(x+3\right)^2\) ( \(5x-3\) chứ sao lại \(5x+3\) )

\(\Leftrightarrow A=\left[\left(5x-3\right)-\left(x+3\right)\right]^2\)

\(\Leftrightarrow A=\left(5x-3-x-3\right)^2\)

\(\Leftrightarrow A=\left(4x-6\right)^2\)

\(\Leftrightarrow A=\left(4x\right)^2-2.4x.6+6^2\)

\(\Leftrightarrow A=16x^2-48x+36\)

b) \(x^3+5x^2+6x\)

\(=x\left(x^2+5x+6\right)\)

\(=x\left(x^2+3x+2x+6\right)\)

\(=x\left[\left(x^2+3x\right)+\left(2x+6\right)\right]\)

\(=x\left[x\left(x+3\right)+2\left(x+3\right)\right]\)

\(=x\left(x+3\right)\left(x+2\right)\)