Math
posted by Anonymous .
a boat starts at point A, moves 3km due north, then 2 km due east, then 1 km due south, and then 4 km due east to point b. Find the distance AB

Add up each component (north or east) separately, and finally find the distance by the vectorial sum (using Pythagoras).
North: 31=2km
East: 2+4=6
Distance = √(2²+6²)
=√(40)
=2√(10) 
I don't understand where for North you put 31. The boat moved 1km South and 3km North. Is that how this was done?

In vectors, directions are signed.
This means that if we take the positive direction as north, then going south is backwards, and is thus represented as negative. Otherwise it would not make a difference between going 3 km north and 1 km north (3+1), and going 3 km north and 1 km south (31).
Hope that clarifies how it's done. 
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