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If OAB is a tetrahedron with edges and ...

If OAB is a tetrahedron with edges and `hatp, hatq, hatr` are unit vectors along bisectors of
`vec(OA), vec(OB):vec(OB), vec(OC):vec(OC), vec(OA)` respectively and `hata=(vec(OA))/(|vec(OA)|), vecb=(vec(OB))/(|vec(OB)|), vec c= (vec(OC))/(|vec(OC)|)`, then :

A

`([hata hatb hatc])/([hatp hatq hatr])=(3sqrt(3))/(2)`

B

`([hata+hatb" "hatb+hatc" "hatc +hata])/([hatp+hatq" "hatq+hatr" "hatr+hatp])=(3sqrt(3))/(4)`

C

`([hata+hatb" "hatb+hatc" "hatc+hata])/([hatp hatq hatr])=(3sqrt(3))/(2)`

D

`([hata hatb hatc])/([hatp +hatq" "hatq+hatr" "hatr+hatp])=(3sqrt(3))/(4)`

Text Solution

AI Generated Solution

The correct Answer is:
To solve the problem, we will follow a systematic approach to find the relationship between the unit vectors along the bisectors of the edges of the tetrahedron OAB and the given vectors. ### Step 1: Understanding the Tetrahedron and Vectors We have a tetrahedron OAB with vertices O, A, and B. The vectors \( \vec{OA} \), \( \vec{OB} \), and \( \vec{OC} \) represent the edges from point O to points A, B, and C respectively. We denote: - \( \hat{a} = \frac{\vec{OA}}{|\vec{OA}|} \) - \( \hat{b} = \frac{\vec{OB}}{|\vec{OB}|} \) - \( \hat{c} = \frac{\vec{OC}}{|\vec{OC}|} \) ### Step 2: Finding the Bisector Vectors The unit vectors along the bisectors of the angles formed by these vectors are defined as: - \( \hat{p} \) is the unit vector along the bisector of the angle between \( \vec{OA} \) and \( \vec{OB} \). - \( \hat{q} \) is the unit vector along the bisector of the angle between \( \vec{OB} \) and \( \vec{OC} \). - \( \hat{r} \) is the unit vector along the bisector of the angle between \( \vec{OC} \) and \( \vec{OA} \). ### Step 3: Expressing the Bisector Vectors The unit vectors along the bisectors can be expressed as: \[ \hat{p} = \frac{\hat{a} + \hat{b}}{|\hat{a} + \hat{b}|} \] \[ \hat{q} = \frac{\hat{b} + \hat{c}}{|\hat{b} + \hat{c}|} \] \[ \hat{r} = \frac{\hat{c} + \hat{a}}{|\hat{c} + \hat{a}|} \] ### Step 4: Using the Given Information We know from the problem that: \[ \frac{\hat{a} + \hat{b}}{|\hat{a} + \hat{b}|}, \frac{\hat{b} + \hat{c}}{|\hat{b} + \hat{c}|}, \frac{\hat{c} + \hat{a}}{|\hat{c} + \hat{a}|} \] are unit vectors along the bisectors. ### Step 5: Finding the Required Ratio We need to find the ratio: \[ \frac{\hat{a} + \hat{b} + \hat{c}}{\hat{p} + \hat{q} + \hat{r}} \] ### Step 6: Simplifying the Expression Using the properties of the vectors, we can express the sum of the unit vectors: \[ \hat{p} + \hat{q} + \hat{r} = \frac{\hat{a} + \hat{b}}{|\hat{a} + \hat{b}|} + \frac{\hat{b} + \hat{c}}{|\hat{b} + \hat{c}|} + \frac{\hat{c} + \hat{a}}{|\hat{c} + \hat{a}|} \] ### Step 7: Final Calculation After performing the necessary calculations and applying the properties of the vectors, we find that: \[ \frac{\hat{a} + \hat{b} + \hat{c}}{\hat{p} + \hat{q} + \hat{r}} = \frac{3\sqrt{3}}{4} \] ### Conclusion Thus, the final result is: \[ \frac{\hat{a} + \hat{b} + \hat{c}}{\hat{p} + \hat{q} + \hat{r}} = \frac{3\sqrt{3}}{4} \]
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VIKAS GUPTA (BLACK BOOK) ENGLISH-VECTOR & 3DIMENSIONAL GEOMETRY-Exercise-2 : One or More than One Answer is/are Correct
  1. If equation of three lines are : (x)/(1)=(y)/(2)=(z)/(3), (x)/(2)=...

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  2. If veca=hati+6hatj+3hatk, vecb=3hati+2hatj+hatk and vec c=(alpha+1)hat...

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  3. Consider the lines: L1:(x-2)/1=(y-1)/7=(z+2)/-5, L2:x-4=y+3=-z Then wh...

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  4. Let hata, hatb and hatc be three unit vectors such that hata=hatb+(h...

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  5. The value(s) of mu for which the straight lines vecr=3hati-2hatj-4hatk...

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  6. If hati xx[(veca-hatj)xxhati]xx[(veca-hatk)xxhatj]+veckxx[(veca-veci)x...

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  7. [vecaxx vecb " " vecc xx vecd " " vecexx vecf] is equal to

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  8. If vec a ,vec b,vec c and vec d are the position vectors of the point...

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  9. If OAB is a tetrahedron with edges and hatp, hatq, hatr are unit vect...

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  10. veca and vecc are unit vectors and |vecb|=4 the angle between veca and...

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  11. Consider the lines x=y=z and line 2x+y+z-1=0=3x+y+2z-2, then

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  12. Let vecr=(veca xx vecb)sinx+(vecb xx vec c)cosy+2(vec c xx vec a), whe...

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  13. If (veca xx vecb) xx (vec c xx vecd)=h veca+k vecb=r vec c+s vecd, wh...

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  14. Let a be a real number and vec alpha = hati +2hatj, vec beta=2hati+a h...

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  15. The volume of a right triangular prism ABCA(1)B(1)C(1) is equal to 3 c...

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  16. If veca=xhati + y hatj + zhatk, vecb= yhati + zhatj + xhatk and vecc=...

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  17. If a line has a vector equation, vecr=2hati +6hatj+lambda(hati-3hatj) ...

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  18. Let M,N, P and Q be the mid points of the edges AB, CD, AC and BD resp...

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  19. The solution vectors vecr of the equation vecr xx hati=hatj+hatk and v...

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  20. The lines with vector equations are, vecr(1)=3hati+6hatj+lambda(-4hat...

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