a,
\(f\left(-1\right)=\left(-1\right)^2-2=1-2=-1\\ f\left(\dfrac{2}{3}\right)=\left(\dfrac{2}{3}\right)^2-2=\dfrac{4}{9}-2=\dfrac{-14}{9}\)
b,
\(y=7\rightarrow x^2-2=7\)
Ta có :
\(x^2-2=7\)
\(\rightarrow x^2=9\)
\(\Rightarrow x=\left\{3;-3\right\}\)