To determine whether the function \( f(x) = x^4 + 3x^2 \) is even, odd, or neither, we can use the definitions of even and odd functions:
- A function \( f(x) \) is even if \( f(-x) = f(x) \) for all \( x \).
- A function \( f(x) \) is odd if \( f(-x) = -f(x) \) for all \( x \).
Let's check \( f(-x) \):
\[ f(-x) = (-x)^4 + 3(-x)^2 \]
Calculating each term:
- \( (-x)^4 = x^4 \)
- \( 3(-x)^2 = 3x^2 \)
Therefore,
\[ f(-x) = x^4 + 3x^2 = f(x) \]
Since \( f(-x) = f(x) \), we conclude that the function \( f(x) = x^4 + 3x^2 \) is even.