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Three-Dimensional Geometry · Question 12 of 120

Question 12

MediumOriginal question

A line makes angles α\alpha, β\beta, γ\gamma with the coordinate axes. What is sin⁡2α+sin⁡2β+sin⁡2γ\sin^{2}\alpha + \sin^{2}\beta + \sin^{2}\gamma?

Options for question 12

Show the answer and explanation
CorrectNot quiteAnswer C

Correct answer: C

Explanation

  1. sin⁡2θ=1−cos⁡2θ\sin^{2}\theta = 1 - \cos^{2}\theta, so the sum is 3−(cos⁡2α+cos⁡2β+cos⁡2γ)3 - (\cos^{2}\alpha + \cos^{2}\beta + \cos^{2}\gamma).

  2. 3−1=23 - 1 = 2.

Worth noting

1 is the sum of the squared cosines, not of the squared sines.

Concept
An identity for direction cosines
Typical time
90 s
Your time
—
The rule this testsDirection cosines of a line
Practise this chapter →

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

Practise this chapter →

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