Advanced Math practice question

Answer: A. −1

x² = 2x + k gives x² − 2x − k = 0, whose discriminant 4 + 4k must be 0: k = −1. (The point is (1, 1).)

Why the other answers are wrong

B. 1

k = 1 gives discriminant 8: two intersections.

C. 0

k = 0 gives x² − 2x = 0: two points, x = 0 and 2.

D. 2

k = 2 gives discriminant 12: two intersections.

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