$2.11 \frac{21}{x^{2}-4 x+10}-x^{2}+4 x=6$.

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$2.11 \frac{21}{x^{2}-4 x+10}-x^{2}+4 x=6$.
2.11 Instruction. Use the substitution $x^{2}-4 x+10=z$ Answer: $x_{1}=1, x_{2}=3$.

