Which function is symmetric with respect to the y -axis?

A function is symmetric with respect to the y-axis when replacing x with −x leaves its output unchanged: f(−x) = f(x). For y = 3x⁶, replacing x by −x gives 3(−x)⁶ = 3x⁶, so the function is unchanged. The other choices have odd powers of x and change sign, so the correct choice is D, y = 3x⁶.

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