Question 1036968
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state triangle and parallelogram law of vector addition
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The &nbsp;<B><I>triangle rule</I></B>&nbsp; of adding vectors: 

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    If the vectors &nbsp;AB and &nbsp;BC are two sides of the triangle &nbsp;ABC, &nbsp;then the sum 
    of the vectors &nbsp;AB&nbsp; and &nbsp;BC&nbsp; (in this order and orientation) &nbsp;is the third side &nbsp;AC&nbsp; of the triangle. 
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The &nbsp;parallelogram rule</I></B>&nbsp; of adding vectors. 

<pre>
    If two vectors &nbsp;AB&nbsp; and &nbsp;AD&nbsp; have the common initial point &nbsp;A, &nbsp;then the sum 
    of the vectors &nbsp;AB&nbsp; and &nbsp;AD&nbsp; is the vector &nbsp;AC&nbsp; which is the diagonal of the parallelogram &nbsp;ADCB 
    built on the sides &nbsp;AB&nbsp; and &nbsp;AD</B>.
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See the lesson <A HREF=https://www.algebra.com/algebra/homework/Vectors/Vectors-in-a-plane.lesson>Vectors in a plane</A> in this site.