a: \(\Leftrightarrow\left(x^2-6x+9\right)^2-15\left(x^2-6x+9+1\right)-1=0\)
\(\Rightarrow\left(x^2-6x+9\right)^2-15\left(x^2-6x+9\right)-16=0\)
\(\Leftrightarrow\left(x^2-6x+9-16\right)\left(x^2-6x+9+1\right)=0\)
\(\Leftrightarrow x^2-6x-7=0\)
=>(x-7)(x+1)=0
=>x=7 hoặc x=-1
b: \(\left(x^2+1\right)^2+3x\left(x^2+1\right)+2x^2=0\)
\(\Leftrightarrow\left(x^2+2x+1\right)\left(x^2+x+1\right)=0\)
\(\Leftrightarrow\left(x+1\right)^2=0\)
=>x+1=0
hay x=-1
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