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If the vectors hat(i)+hat(j)+hat(k) make...

If the vectors `hat(i)+hat(j)+hat(k)` makes angle `alpha, beta and gamma` with vectors `hat(i), hat(j) and hat(k)` respectively, then

A

`alpha=beta ne gamma`

B

`alpha=gammanebeta`

C

`beta=gammanealpha`

D

`alpha=beta=gamma`

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The correct Answer is:
To solve the problem, we need to find the relationship between the angles \( \alpha \), \( \beta \), and \( \gamma \) that the vector \( \hat{i} + \hat{j} + \hat{k} \) makes with the unit vectors \( \hat{i} \), \( \hat{j} \), and \( \hat{k} \) respectively. ### Step-by-Step Solution: 1. **Define the Vector:** Let \( \mathbf{A} = \hat{i} + \hat{j} + \hat{k} \). 2. **Calculate the Magnitude of Vector \( \mathbf{A} \):** \[ |\mathbf{A}| = \sqrt{1^2 + 1^2 + 1^2} = \sqrt{3} \] 3. **Calculate the Dot Product with \( \hat{i} \):** The angle \( \alpha \) is defined such that: \[ \mathbf{A} \cdot \hat{i} = |\mathbf{A}| |\hat{i}| \cos \alpha \] Substituting the values: \[ \hat{i} + \hat{j} + \hat{k} \cdot \hat{i} = 1 \cdot \sqrt{3} \cdot 1 \cdot \cos \alpha \] This simplifies to: \[ 1 = \sqrt{3} \cos \alpha \] Thus, \[ \cos \alpha = \frac{1}{\sqrt{3}} \] 4. **Calculate the Dot Product with \( \hat{j} \):** Similarly, for angle \( \beta \): \[ \mathbf{A} \cdot \hat{j} = |\mathbf{A}| |\hat{j}| \cos \beta \] This gives: \[ \hat{i} + \hat{j} + \hat{k} \cdot \hat{j} = 1 \cdot \sqrt{3} \cdot 1 \cdot \cos \beta \] Simplifying: \[ 1 = \sqrt{3} \cos \beta \] Thus, \[ \cos \beta = \frac{1}{\sqrt{3}} \] 5. **Calculate the Dot Product with \( \hat{k} \):** For angle \( \gamma \): \[ \mathbf{A} \cdot \hat{k} = |\mathbf{A}| |\hat{k}| \cos \gamma \] This gives: \[ \hat{i} + \hat{j} + \hat{k} \cdot \hat{k} = 1 \cdot \sqrt{3} \cdot 1 \cdot \cos \gamma \] Simplifying: \[ 1 = \sqrt{3} \cos \gamma \] Thus, \[ \cos \gamma = \frac{1}{\sqrt{3}} \] 6. **Establish the Relationship Between Angles:** Since we have: \[ \cos \alpha = \cos \beta = \cos \gamma = \frac{1}{\sqrt{3}} \] This implies that: \[ \alpha = \beta = \gamma \] ### Conclusion: The angles \( \alpha \), \( \beta \), and \( \gamma \) are equal. ### Final Answer: \[ \alpha = \beta = \gamma \]
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ARIHANT MATHS ENGLISH-PRODUCT OF VECTORS-Exercise (Single Option Correct Type Questions)
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  4. (r*hat(i))^(2)+(r*hat(j))^(2)+(r*hat(k))^(2) is equal to

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  5. If hat a and hatb are two unit vectors inclined at an angle theta, the...

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  6. If vec A=4 hat i+6 hat ja n d vec B=3 hat j+4 hat k , then find the c...

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  7. If vectors a=2hat(i)-3hat(j)+6hat(k) and vector b=-2hat(i)+2hat(j)-hat...

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  8. If veca and vecb are two vectors , then prove that (vecaxxvecb)^(2)=|{...

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  9. The moment of the force F acting at a point P, about the point C is

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  10. The moment of a force represented by F=hat(i)+2hat(j)+3hat(k) about th...

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  11. A force of magnitude 6 acts along the vector (9, 6, -2) and passes thr...

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  12. A force F=2hat(i)+hat(j)-hat(k) acts at point A whose position vector...

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  13. If a, b and c are any three vectors and their inverse are a^(-1), b^(-...

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  14. If a, b and c are three non-coplanar vectors, then find the value of (...

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  15. atimes(btimesc) is coplanar with

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  16. If u=hat(i)(atimeshat(i))+hat(j)(atimeshat(j))+hat(k)(atimeshat(k)), t...

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  17. If a=hat(i)+2hat(j)-2hat(k), b=2hat(i)-hat(j)+hat(k) and c=hat(i)+3hat...

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  18. If atimes(btimesc)=0, then

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  19. A vectors which makes equal angles with the vectors 1/3(hati - 2hatj ...

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  20. [Find by vector method the horizontal force and the force inclined at ...

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