Given a vector < a, b >,
it has components a and b (think of these as legs of a right triangle). Finding the magnitude of a vector boils down to finding the hypotenuse of that right triangle.
So we go to our handy dandy Pythagorean Theorem:
\(\rm a^2 + b^2 = c^2\)
Solving for the hypotenuse, taking the square root,
\(\rm \sqrt{a^2+b^2}=c\)
This thing I'm calling c is the magnitude of the vector < a, b >.
