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Three-Dimensional Geometry · Question 99 of 120

Question 99

MediumOriginal question

The lines r⃗=(i^+3j^−6k^)+λ(i^−j^+2k^)\vec{r} = (\hat{i} + 3\hat{j} - 6\hat{k}) + \lambda(\hat{i} - \hat{j} + 2\hat{k}) and r⃗=(i^−2k^)+μ(2i^+j^)\vec{r} = (\hat{i} - 2\hat{k}) + \mu(2\hat{i} + \hat{j}) intersect. At which point?

Options for question 99

Show the answer and explanation
CorrectNot quiteAnswer B

Correct answer: B

Explanation

  1. Equate the components: 1+λ=1+2μ1 + \lambda = 1 + 2\mu, 3−λ=μ3 - \lambda = \mu and −6+2λ=−2-6 + 2\lambda = -2.

  2. The last gives λ=2\lambda = 2, then μ=1\mu = 1, and the first checks: 3=33 = 3. The point is (3,1,−2)(3, 1, -2).

Worth noting

(5,2,−2)(5, 2, -2) puts λ=2\lambda = 2 into the second line, whose parameter is μ\mu.

Concept
When and where two lines meet
Typical time
90 s
Your time
—
The rule this testsSkew lines and the shortest distance
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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.