[tex]\bf f(x)=x^2\qquad f(4-\sqrt{2})\implies x=4-\sqrt{2}
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f(4-\sqrt{2})=\left( 4-\sqrt{2} \right)^2\implies f(4-\sqrt{2})=\left( 4-\sqrt{2} \right)\left( 4-\sqrt{2} \right)[/tex]
do a FOIL on it to get the product, or just use the binomial theorem to expand the binomial and simplify
