What is the correct expression for \vec{OP}?

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Homework Help Overview

The discussion revolves around vector expressions in the context of a triangle OAB, where vectors \(\vec{OA}\) and \(\vec{OB}\) are defined as \(a\) and \(b\) respectively. The problem involves finding expressions for various vectors related to points P and Q on line segment AB.

Discussion Character

  • Exploratory, Mathematical reasoning, Problem interpretation

Approaches and Questions Raised

  • The original poster attempts to express vectors \(\vec{BA}\), \(\vec{PB}\), and \(\vec{OP}\) in terms of \(a\) and \(b\). Some participants question the correctness of the original poster's calculations, particularly regarding the expression for \(\vec{OP}\).

Discussion Status

Participants are actively discussing the expressions for the vectors, with some providing insights into the calculations. There is recognition of a potential error in the original poster's approach, and further calculations are being shared to clarify the correct expression for \(\vec{OP}\).

Contextual Notes

The original poster indicates a lack of understanding due to missing class content, which may affect their grasp of the vector concepts being discussed.

Argyron
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I missed 2 weeks of class where we were introduced to vectors and now I have to learn it by myself from the book. I'm stuck on this problem that's part of the assigned homework. If anyone could help me that would be great thanks.
I'm sorry if it's a stupid mistake :/

Homework Statement


In triangle OAB, \vec{OA} = a and \vec{OB} = b
P is a point on AB such that \vec{AP} = 2\vec{PB}
and Q is a point such that \vec{OP} = 3\vec{PQ}

Express the following in terms of a and b.
a) \vec{BA}
b) \vec{PB}
c) \vec{OP}
d) \vec{PQ}
e) \vec{BQ}

Homework Equations


N/A

The Attempt at a Solution


a) \vec{BA} = a-b
b) \vec{PB} = 1/3(b-a)

I got stuck on c)
My working out is
\vec{OP} = \vec{OB} + \vec{BP} [Express both vectors in a and b]
\vec{OP} = b + 1/3(a-b)
But when I check my answer the book said it was:
1/3(a+2b)

Where did I go wrong?
 
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Argyron said:
I missed 2 weeks of class where we were introduced to vectors and now I have to learn it by myself from the book. I'm stuck on this problem that's part of the assigned homework. If anyone could help me that would be great thanks.
I'm sorry if it's a stupid mistake :/

Homework Statement


In triangle OAB, \vec{OA} = a and \vec{OB} = b
P is a point on AB such that \vec{AP} = 2\vec{PB}
and Q is a point such that \vec{OP} = 3\vec{PQ}

Express the following in terms of a and b.
a) \vec{BA}
b) \vec{PB}
c) \vec{OP}
d) \vec{PQ}
e) \vec{BQ}

Homework Equations


N/A

The Attempt at a Solution


a) \vec{BA} = a-b
b) \vec{PB} = 1/3(b-a)

I got stuck on c)
My working out is
\vec{OP} = \vec{OB} + \vec{BP} [Express both vectors in a and b]
\vec{OP} = b + 1/3(a-b)
But when I check my answer the book said it was:
1/3(a+2b)

Where did I go wrong?

Solve it further.
\vec{OP} = b + 1/3(a-b)=b+a/3-b/3=a/3+2b/3
 
Pranav-Arora said:
Solve it further.
\vec{OP} = b + 1/3(a-b)=b+a/3-b/3=a/3+2b/3

That seems so obvious now that I see it. Thanks for that.
 
Argyron said:
That seems so obvious now that I see it. Thanks for that.

You are welcome! :smile:

Did you solve the rest of the questions?
 
Pranav-Arora said:
You are welcome! :smile:

Did you solve the rest of the questions?

Yeah, it was easy once I had c. :smile:
 

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