A mirror has a parabolic surface defined by the equation y is equal to 1 over 24 x squared with the vertex open paren 0 comma 0 close paren at the center of the mirror. When the width of the mirror is 8 inches, what is the depth, y , of the mirror?

The mirror is 8 inches wide, so the distance from its center (the vertex) to either edge is 8 ÷ 2 = 4 inches. Substitute x = 4 into y = x²/24: y = 4²/24 = 16/24 = 2/3 inch. The depth is 2/3 inch, choice B.

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