Final answer:
The landowner must use vector addition to determine the third side of her triangular plot of land by constructing a parallelogram with the given displacement vectors and measuring the diagonal opposite the starting corner.
Step-by-step explanation:
The question is about calculating the length and orientation of the third side of a triangle when the other two sides are given as displacement vectors. This problem involves using vector addition to find the resulting vector which represents the third side of the triangular land that is to be fenced. To solve this, vector A and vector B must be added head-to-tail, and then the length and direction of the resultant vector C can be determined using a ruler and protractor. The landowner can calculate this by constructing a parallelogram with the two given vectors as adjacent sides. The third side, C, will be the diagonal of this parallelogram that is opposite the starting corner.