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in 3D Coordinate Geometry by (29.3k points)
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Write the inclination of a line with Z-axis, if its direction ratios are proportional to 0, 1, –1.

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Given, the direction ratios of the line are proportional to (0, 1, -1)

Therefore, consider the direction ratios of the give line can be

a = 0 × k, b = 1 × k, c = (-1) × k

[where k is some proportionality constant]

Now the direction ratios of the line are

a = 0, b = k, c = -k

As we know the direction cosine of z-axis can be given by

cos γ = n = \(\frac{c}{\sqrt{a^2+b^2+c^2}}\) where γ is the angle made by the line with the z-axis.

By using the above formula:

[As cosine function is negative, the angle become 135° instead of 45°]

\(\gamma = \frac{3\pi}{4}\)

The inclination of the line with z-axis is \(\frac{3\pi}{4}\)

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