Vladas believes that an equation with a squared term is never a function of x. Which equation can be used to show Vladas that his hypothesis is incorrect?

An equation describes y as a function of x when each x-value gives exactly one y-value. In choice B, x² − y = 25 rearranges to y = x² − 25, so every x gives one y, even though the equation contains a squared term. The other choices can give more than one y-value for some x-values.

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