The vector AB with the end at point B (1,11) has coordinates (12,20). Find the abscissa of point A.

If the vector starts at point A and ends at point B, then the coordinates of the vector will be the differences of the corresponding coordinates of the points:

AB = (XB – XA, YB – YA) = (1 – XA, 20 – YB)

We know that XB – XA = 12, besides, we know the coordinate of the end point XB = 1. After substituting the value of XB, we get:

1 – XA = 12.

Answer: XA = -11.

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