b)\(x^2-7x+6=x^2-6x-x+6\)

                          \(=x\left(x-6\right)-\left(x-6\right)\)

                             \(=\left(x-1\right)\left(x-6\right)\)

Câu a khó hiểu quá

\(giải:\)

\(1,\)\(\frac{x}{5}+\frac{2x+1}{3}=\frac{x-5}{15}\)

\(\Leftrightarrow\frac{x}{5}+\frac{2x+1}{3}-\frac{x-15}{15}=0\)

\(\Leftrightarrow\frac{3x}{15}+\frac{5\left(2x+1\right)}{15}-\frac{x-15}{15}=0\)

\(\Leftrightarrow\frac{3x+5\left(2x+1\right)-\left(x-15\right)}{15}=0\)

\(\Leftrightarrow\frac{3x+10x+5-x+15}{15}=0\)

\(\Leftrightarrow\frac{12x+20}{15}=0\)

\(\Rightarrow12x+20=0\)

\(\Leftrightarrow12x=-20\Leftrightarrow x=\frac{-5}{3}\)

vậy tập nghiệm của phương trình là \(s=\left[\frac{-5}{3}\right]\)

\(2,\)\(\left(x^3-64\right)+6x\left(x-4\right)=0\)

\(\Leftrightarrow\left(x^3-4^3\right)+6x\left(x-4\right)=0\)

\(\Leftrightarrow\left(x-4\right)\left(x^2+4x+16\right)+6x\left(x-4\right)=0\)

\(\Leftrightarrow\left(x-4\right)\left(x^2+4x+16+6x\right)=0\)

\(\Leftrightarrow\left(x-4\right)\left(x^2+10x+16\right)=0\)

 \(mà\)\(x^2+10x+16>0\)

\(\Rightarrow x-4=0\Rightarrow x=4\)

vậy x=4 là nghiệm của phương trình

\(3,\)\(\frac{x+2}{x-2}-\frac{x-2}{x+2}=\frac{16}{x^2-4}\)

\(\Leftrightarrow\frac{x+2}{x-2}-\frac{x-2}{x+2}=\frac{16}{\left(x-2\right)\left(x+2\right)}\)

\(\Leftrightarrow\frac{\left(x+2\right)\left(x+2\right)}{\left(x-2\right)\left(x+2\right)}-\frac{\left(x-2\right)\left(x-2\right)}{\left(x+2\right)\left(x-2\right)}=\frac{16}{\left(x-2\right)\left(x+2\right)}\)

\(\Rightarrow\left(x+2\right)\left(x+2\right)-\left(x-2\right)\left(x-2\right)=16\)\

\(\Leftrightarrow\left(x+2\right)^2-\left(x-2\right)^2-16=0\)

\(\Leftrightarrow x^2+4x+4-x^2+4x-4-16=0\)

\(\Leftrightarrow8x-16=0\)

\(\Leftrightarrow8\left(x-2\right)=0\)

\(\Leftrightarrow x-2=0\)

\(\Leftrightarrow x=2\)

vậy x=2 là nghiệm của phương trình

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