Deepak Patra
Last Activity: 16 Years ago

The formula for the length OP or |p| is a kind of 3 dimensional form of Pythagoras' theorem.
Here's how the working would go if we had a = 4 and b = 3 and c = 12.
Using Pythagoras' theorem in the yellow right-angled triangle we get
OQ = the square root of (16 + 9) = 5
and then, using Pythagoras' theorem in the vertical green right-angled triangle, we get
OP = the square root of (25 + 144) = 13.
Alternatively, in just one step of working, we have
OP = the square root of (16 + 9 + 144) = 13.