Identify the function in which y varies directly with x. y = x y = 9x + 9 y = 0x y = 9x − 9

The equation in which y varies directly with x is y = x.

This is because no matter what value of x we put in, we get the same y. So when we change x, y changes directly. No other equation has that same fact. As a result, this is the only direct variation.

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