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UPSC NDA I 2019 Mathematics Solved Paper

Question : 65 of 120

Marks: +1, -0

What are the direction cosines of z-axis?

Solution:

Concept:

Direction cosines are the cosines of the angles a line makes with the positive

x

y

, and

z

axes.

Explanation:

The

z

-axis makes angles of

90^\circ

with the

x

-axis and

y

-axis, and

0^\circ

with the

z

-axis.

Thus, the direction cosines are

\cos 90^\circ = 0

\cos 90^\circ = 0

, and

\cos 0^\circ = 1

These are written as

\langle 0, 0, 1 \rangle

Answer:

\langle 0, 0, 1 \rangle

(Option D).

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