If (x, y) are the coordinates of a point p in the xy-plane, then x is called the of p and y is the of p.

The first coordinate of a point P is called the x-coordinate of P, 

and the second coordinate of a point P is called the y-coordinate of P.

So 

"x is called the ___x-coordinate of p and y is the ___y-coordinate of p."

x-coordinate
y-coordinate

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