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Three-Dimensional Geometry · Question 48 of 120

Question 48

MediumOriginal question

Which point of the line x−22=y+3−2=z−11\frac{x - 2}{2} = \frac{y + 3}{-2} = \frac{z - 1}{1} is at a distance of 6 from (2,−3,1)(2, -3, 1) and has z>1z > 1?

Options for question 48

Show the answer and explanation
CorrectNot quiteAnswer B

Correct answer: B

Explanation

  1. A point of the line is (2+2λ,−3−2λ,1+λ)(2 + 2\lambda, -3 - 2\lambda, 1 + \lambda), at distance 4+4+1 ∣λ∣=3∣λ∣\sqrt{4 + 4 + 1}\,\lvert \lambda \rvert = 3\lvert \lambda \rvert from (2,−3,1)(2, -3, 1).

  2. 3∣λ∣=63\lvert \lambda \rvert = 6 gives λ=±2\lambda = \pm 2, and z>1z > 1 needs λ=2\lambda = 2: the point (6,−7,3)(6, -7, 3).

Worth noting

(14,−15,7)(14, -15, 7) takes λ=6\lambda = 6, but each unit of λ\lambda moves 3 units along the line, not 1.

Concept
A point at a given distance along a line
Typical time
90 s
Your time
—
The rule this testsThe equation of a line
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Ten questions from Three-Dimensional Geometry, at your own pace.

Practise this chapter →

Ten questions from Three-Dimensional Geometry, at your own pace.