The point A is translated to the point B by the vector (4u above 3u).

|AB| (with arrow on top of AB) = 12.5

I have seen people work this out by doing:

4u^2 + 3u^2 = 12.5^2

16u^2 + 9u^2 = 12.5^2

u = square root of 12.5^2/25

My question is: How do you know that you have to square 4u and 3u??

- Thanks!