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    Given that a= 2i + 5j and b= 3i - j, find

    P if a+Pb is parallel to the vector i

    Solution:

    a+Pb= (2i+5j) + P(3i-j)=(2+3P)i + (5-P)j
    Parallel to i, so 5-P=0, P=5.

    I don't get the part about the vector being parallel to i. Why is the bracket made equal to 0? And why only that bracket and not the other one?

    Thanks
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    (Original post by ms94uk)
    So they ask for paralled vectors to i so surely both i components must be the same so you need you multiply b by some sort of constant to achieve it do you get it or still nothing?
    No I don't get it as we rushed through vectors in class and our teacher didn't teach it well
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    Well, if it is parallel to i, surely the j component is 0. If it were not 0, it wouldn't be parallel to i
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    If you have two vectors, and you are trying to make a+ (X)b where (X) is a const. Calculate then that gives you : 2i+5j + (X) (3i-j) now collect same i and j terms so you get 2+ 3(X) i + 5-1(X)j if its parallel to i that means it must be flat since i is horizontal so surely j component must be zero but because our j component is 5-1(X) therefore 5-1(X)=0, (X)=5

    Remember i is one unit to the left and j is one unit upwards so if vector is moving parallel to i that means is a flat line eg 14i it cant have j component because j component would make it move up or down and it must continue moving in a same straight line as x axis or i component

    Get it now?
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    (Original post by ms94uk)
    If you have two vectors, and you are trying to make a+ (X)b where (X) is a const. Calculate then that gives you : 2i+5j + (X) (3i-j) now collect same i and j terms so you get 2+ 3(X) i + 5-1(X)j if its parallel to i that means it must be flat since i is horizontal so surely j component must be zero but because our j component is 5-1(X) therefore 5-1(X)=0, (X)=5

    Remember i is one unit to the left and j is one unit upwards so if vector is moving parallel to i that means is a flat line eg 14i it cant have j component because j component would make it move up or down and it must continue moving in a same straight line as x axis or i component

    Get it now?
    Thanks a lot I get it now
 
 
 
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