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

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The discussion revolves around solving vector problems in triangle OAB, specifically focusing on the expression for \vec{OP}. The user, who missed two weeks of class, initially struggled with the calculations but found clarity after breaking down the vector relationships. The correct expression for \vec{OP} was derived as 1/3(a + 2b), correcting the user's earlier mistake. Once this was resolved, the user reported that the remaining questions became easier to solve. The exchange highlights the importance of understanding vector relationships in geometry.
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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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