Which value must be added to the expression x squared minus 3 x to make it a perfect-square trinomial?

To complete the square for x² − 3x, take half of the coefficient of x, which is −3/2, and square it: (−3/2)² = 9/4. Adding 9/4 gives x² − 3x + 9/4 = (x − 3/2)², a perfect-square trinomial. The correct choice is 9/4.

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