Problem
ALG-B1-M03-P002 The Substitution \(u=x^2\)
#2
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Solve \(x^4-10x^2+9=0\).
Set \(u=x^2\), remembering that \(u\ge0\).
Let \(u=x^2\). Then \(u^2-10u+9=0\), so \(u=1\) or \(u=9\).
Thus \(x=\pm1\) or \(x=\pm3\).
After the substitution one must return to \(x\).