How to Find λ in a Triangle with Given Vectors OA, OB, P, and Q?

In summary, the conversation discusses finding the value of λ in the equation BG = λ BP, given that OA = 5s, OB = 10t, P is on the middle of OA, and AQ = 3/4 QB. The conversation includes equations for AB, BQ, OQ, and BP in terms of s and t, and the final value of λ is determined to be 2/5. The conversation also provides a hint to use simultaneous equations to solve for λ.
  • #1
songoku
2,306
327

Homework Statement


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Given that:
OA = 5s
OB = 10 t
P is on the middle of OA and AQ = 3 QB

Find λ if BG = λ BP


Homework Equations


basic vector


The Attempt at a Solution


I have found AB, BQ, OQ, BP; all in terms of s and t. How to find λ? I've tried but always came back to equation BP = BP or 0 = 0. Please give me hint to start

Thanks
 
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  • #2


If you have found AB then you must have some information you have not given here.
The length AB depends not only on the lengths of OA and OB but also on the angle between them.

(There is no "B" in your picture. I assume it is the third vertex of the triangle.
 
  • #3


HallsofIvy said:
If you have found AB then you must have some information you have not given here.
The length AB depends not only on the lengths of OA and OB but also on the angle between them.

(There is no "B" in your picture. I assume it is the third vertex of the triangle.

Yes, the third vertex is B. This is my work:
AB = AO + OB = -5 s + 10 t

Sorry I didn't explain it clearly. I didn't find the length but I found the vector.

BQ = 1/4 BA = 1/4 (5s - 10t)

OQ = OA + AQ = 5 s + 3/4 (10t - 5s) = 5/4 (6t + s)

BP = BO + OP = -10t + 5/2 s

By the way, the value of λ should be 2/5. Thanks
 
  • #4


songoku said:
Yes, the third vertex is B. This is my work:
AB = AO + OB = -5 s + 10 t

Sorry I didn't explain it clearly. I didn't find the length but I found the vector.

BQ = 1/4 BA = 1/4 (5s - 10t)

OQ = OA + AQ = 5 s + 3/4 (10t - 5s) = 5/4 (6t + s)

BP = BO + OP = -10t + 5/2 s

By the way, the value of λ should be 2/5. Thanks

That looks to be a good start. Now, let OG=μ OQ, then OQ = OA + AQ and after some algebra work. OQ = 5/4 s + 30/4 t

BG = λ [5/2 s - 10t ]

OG + GB = OB
5/4 μs + 30/4 μt + 10 λt - 5/2 λs = 10t and by comparing...

30/4 μ + 10 λ = 10 --- 1
5/4 μ -5/2 λ =0 ---2

Now you are left to solve the simultaneous equations. :smile:Hope that helps.
 
  • #5


Ah damn, didn't think about elimination.

Thanks. That helps a lot
 

Related to How to Find λ in a Triangle with Given Vectors OA, OB, P, and Q?

1. How do I find the magnitude of a vector in a triangle?

To find the magnitude of a vector in a triangle, you can use the Pythagorean theorem. This theorem states that the square of the hypotenuse (the side opposite the right angle) is equal to the sum of the squares of the other two sides. In a triangle, the magnitude of a vector is equal to the length of the side opposite the angle it forms with the x-axis.

2. What is the formula for finding the direction of a vector in a triangle?

The direction of a vector in a triangle can be found by using the tangent function. The tangent of an angle is equal to the ratio of the opposite side to the adjacent side. In other words, the direction of a vector is the slope of the line connecting its starting point to its endpoint.

3. Is there a way to find the components of a vector in a triangle?

Yes, the components of a vector in a triangle can be found using trigonometric functions. The x-component of a vector can be calculated by multiplying its magnitude by the cosine of the angle it forms with the x-axis. Similarly, the y-component can be found by multiplying the magnitude by the sine of the angle.

4. Can vectors in a triangle be negative?

Yes, vectors in a triangle can have negative components. This means that the vector is pointing in the opposite direction of the positive axis. However, the magnitude of the vector will always be positive.

5. How do I find the resultant vector in a triangle?

The resultant vector in a triangle can be found by adding the x-components and y-components of all the given vectors. This will give you the x-component and y-component of the resultant vector. The magnitude of the resultant vector can then be found using the Pythagorean theorem, and the direction can be calculated using the tangent function.

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