Question
\[f\left( x \right) = \left\{ \begin{array}{l}
4,\,x < - 1\\
- 4x,\, - 1 \le x \le 0.
\end{array} \right.\]
If $$f\left( x \right)$$ is an even function in $$R$$ then the definition of $$f\left( x \right)$$ in $$\left( {0,\, + \infty } \right)$$ is :
A.
\[f\left( x \right) = \left\{ \begin{array}{l}
4x,\,0 < x \le 1\\
4x,\,x > 1
\end{array} \right.\]
B.
\[f\left( x \right) = \left\{ \begin{array}{l}
4x,\,0 < x \le 1\\
- 4,\,x > 1
\end{array} \right.\]
C.
\[f\left( x \right) = \left\{ \begin{array}{l}
4,\,0 < x \le 1\\
4x,\,x > 1
\end{array} \right.\]
D.
none of these
Answer :
\[f\left( x \right) = \left\{ \begin{array}{l}
4x,\,0 < x \le 1\\
4x,\,x > 1
\end{array} \right.\]
Solution :
An even function is symmetrical about the $$y$$-axis.
Clearly from the graph, the definition given in option (A) is correct.