Advanced MathHardSum of the x-intercepts of a cubic
Advanced Math practice question
In the xy-plane, the graph of f(x) = x³ − 4x crosses the x-axis at three points. What is the sum of the x-coordinates of those three points?
Answer: 0
x³ − 4x = x(x − 2)(x + 2), so the x-intercepts are 0, 2, and −2. Their sum is 0.
Common wrong answers
- If you answered 2
- 2 is one intercept.
- If you answered 4
- 4 is the sum of the two nonzero intercepts' absolute values.
- If you answered -4
- −4 is the coefficient of x, not a sum of intercepts.
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