Question

[Lê Chấn Long]

mn giúp em đc k ạ

Answer 1

[Đoàn Đức Hà]

Bài 2. 

a) \(\left(x+2\right)\left(x^2-2x+4\right)-x\left(x+3\right)\left(x-3\right)=26\)

\(\Leftrightarrow x^3+8-x\left(x^2-9\right)=26\)

\(\Leftrightarrow9x=18\)

\(\Leftrightarrow x=2\).

b) \(\left(4x+1\right)\left(1-4x+16x^2\right)-16x\left(4x^2-5\right)=17\)

\(\Leftrightarrow64x^3+1-64x^3+80x=17\)

\(\Leftrightarrow80x=16\)

\(\Leftrightarrow x=\frac{1}{5}\)

c) \(\left(x+3\right)^3-x\left(3x+1\right)^2+\left(2x+1\right)\left(4x^2-2x+1\right)-3x^2=54\)

\(\Leftrightarrow x^3+9x^2+27x+27-9x^3-6x^2-x+8x^3+1-3x^2=54\)

\(\Leftrightarrow26x=26\)

\(\Leftrightarrow x=1\)

d) \(7x^3+3x^2-3x+1=0\)

\(\Leftrightarrow8x^3=x^3-3x^2+3x-1\)

\(\Leftrightarrow\left(2x\right)^3=\left(x-1\right)^3\)

\(\Leftrightarrow2x=x-1\)

\(\Leftrightarrow x=-1\)

e) \(x^2-6x-7=0\)

\(\Leftrightarrow\left(x-7\right)\left(x+1\right)=0\)

\(\Leftrightarrow\orbr{\begin{cases}x=7\\x=-1\end{cases}}\)

f) \(4x^2-8x+4y^2+4y+5=0\)

\(\Leftrightarrow4x^2-8x+4+4y^2+4y+1=0\)

\(\Leftrightarrow4\left(x-1\right)^2+\left(2y+1\right)^2=0\)

\(\Leftrightarrow\hept{\begin{cases}x-1=0\\2y+1=0\end{cases}}\Leftrightarrow\hept{\begin{cases}x=1\\y=-\frac{1}{2}\end{cases}}\)

g) \(x^2+5y^2-4xy-2y+1=0\)

\(\Leftrightarrow x^2-4xy+4y^2+y^2-2y+1=0\)

\(\Leftrightarrow\left(x-2y\right)^2+\left(y-1\right)^2=0\)

\(\Leftrightarrow\hept{\begin{cases}x-2y=0\\y-1=0\end{cases}}\Leftrightarrow\hept{\begin{cases}x=2\\y=1\end{cases}}\)