Advanced Math practice question

Answer: A. 4

One touch means discriminant 0: 16 − 4c = 0, c = 4. Then y = (x + 2)².

Why the other answers are wrong

B. −4

c = −4 gives discriminant 32: two crossings.

C. 2

c = 2 gives discriminant 8: two crossings.

D. 16

c = 16 gives a negative discriminant: no crossings.

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