Question

cho hàm số y=f(x)=-x^2 + 2. tìm x để f(x)=-2. giá trị x=

Answer 1

Ta có: \(y=f\left(x\right)=-x^2+2\)

Thay \(f\left(x\right)=-2\)

\(\Rightarrow-2=-x^2+2\)

\(\Rightarrow-4=-x^2\)

\(\Rightarrow x^2=4\)

\(\Rightarrow x=\pm2\)

Vậy \(x=\pm2\)

Answer 2

\(f\left(x\right)=-2\)

\(\Leftrightarrow-x^2+2=-2\)

\(\Leftrightarrow-x^2=-2-2=-4\)

\(\Leftrightarrow x^2=4\)

\(\Leftrightarrow\left[\begin{matrix}x=2\\x=-2\end{matrix}\right.\)