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Continuity & Differentiability · Question 55 of 125

Question 55

HardOriginal question

For which values of kk is f(x)={k2x,x<2x+3k,x≥2f(x) = \begin{cases} k^{2}x, & x < 2 \\ x + 3k, & x \ge 2 \end{cases} continuous at x=2x = 2?

Options for question 55

Show the answer and explanation
CorrectNot quiteAnswer D

Correct answer: D

Explanation

  1. The pieces must meet at x=2x = 2: 2k2=2+3k2k^{2} = 2 + 3k.

  2. 2k2−3k−2=(2k+1)(k−2)=02k^{2} - 3k - 2 = (2k + 1)(k - 2) = 0, so k=2k = 2 or k=−12k = -\frac{1}{2}.

Worth noting

k=2k = 2 alone drops the second root; k=−12k = -\frac{1}{2} also makes both pieces 12\frac{1}{2} at x=2x = 2.

Concept
A constant from a quadratic condition
Typical time
120 s
Your time
—
The rule this testsChoosing a constant for continuity
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Ten questions from Continuity & Differentiability, at your own pace.

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Ten questions from Continuity & Differentiability, at your own pace.