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The direction cosines of a line equally ...

The direction cosines of a line equally inclined to the axes are:

A

`(1)/(3),(1)/(3) , (1)/(3)`

B

`-(1)/(3), (1)/(3) , (1)/(3)`

C

`(1)/(sqrt3),(1)/(sqrt3), (1)/(sqrt3)`

D

`-(1)/(sqrt3),- (1)/(sqrt3), -(1)/(sqrt3)`

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The correct Answer is:
To find the direction cosines of a line that is equally inclined to the coordinate axes, we can follow these steps: ### Step-by-Step Solution: 1. **Understanding Direction Cosines**: The direction cosines of a line are denoted as \( l \), \( m \), and \( n \), which correspond to the angles \( \alpha \), \( \beta \), and \( \gamma \) that the line makes with the x-axis, y-axis, and z-axis respectively. 2. **Equally Inclined Condition**: Since the line is equally inclined to the axes, we have: \[ \cos \alpha = \cos \beta = \cos \gamma \] This implies: \[ l = m = n \] 3. **Using the Identity**: We know from the properties of direction cosines that: \[ l^2 + m^2 + n^2 = 1 \] Substituting \( l = m = n \) into this equation gives: \[ l^2 + l^2 + l^2 = 1 \] Simplifying this, we get: \[ 3l^2 = 1 \] 4. **Solving for \( l \)**: Dividing both sides by 3: \[ l^2 = \frac{1}{3} \] Taking the square root of both sides: \[ l = \pm \frac{1}{\sqrt{3}} \] 5. **Finding Direction Cosines**: Since \( l = m = n \), we have: \[ l = m = n = \frac{1}{\sqrt{3}} \quad \text{or} \quad l = m = n = -\frac{1}{\sqrt{3}} \] Therefore, the direction cosines of the line are: \[ \left( \frac{1}{\sqrt{3}}, \frac{1}{\sqrt{3}}, \frac{1}{\sqrt{3}} \right) \quad \text{and} \quad \left( -\frac{1}{\sqrt{3}}, -\frac{1}{\sqrt{3}}, -\frac{1}{\sqrt{3}} \right) \] ### Final Answer: The direction cosines of a line equally inclined to the axes are: \[ \left( \frac{1}{\sqrt{3}}, \frac{1}{\sqrt{3}}, \frac{1}{\sqrt{3}} \right) \quad \text{and} \quad \left( -\frac{1}{\sqrt{3}}, -\frac{1}{\sqrt{3}}, -\frac{1}{\sqrt{3}} \right) \]
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