Question:medium

If the focus of the parabola \[ (y - k)^2 = 4(x - h) \] always lies between the lines \(x + y = 1\) and \(x + y = 3\) then:

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Understanding how a parabola’s focus is derived from its equation is key to solving locus-related problems.
Updated On: Jan 13, 2026
  • \(0<h + k<2\)
  • \(0<h + k<1\)
  • \(1<h + k<2\)
  • \(1<h + k<3\)
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The Correct Option is A

Solution and Explanation

The standard form of the parabola is \[(y - k)^2 = 4(x - h)\]The focus is located at \[(h + 1, k)\]Given that the focus lies between the lines \(x + y = 1\) and \(x + y = 3\), substituting the focus coordinates into these inequalities yields:\[1<(h+1) + k<3\]This simplifies to:\[0<h + k<2\]Therefore, the range for \( h + k \) is:\[0<h + k<2\]
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