The Dot Product
2. Unveiling the Secret Weapon
Here’s the real key to determining if two vectors are perpendicular: the dot product. Now, I know what you might be thinking: “Dot product? Sounds scary!” But trust me, it’s not nearly as intimidating as it sounds. In fact, it’s a rather friendly calculation that gives us a lot of information about the relationship between two vectors.
The dot product of two vectors, A and B, is calculated like this: A B = |A| |B| cos(), where |A| and |B| are the magnitudes (lengths) of the vectors, and (theta) is the angle between them. Now, here’s the kicker: if A and B are perpendicular, then is 90 degrees. And what’s the cosine of 90 degrees? Zero!
This means that if A and B are perpendicular, their dot product will always be zero. Always, always, always. This gives us a neat little way to test for perpendicularity. Calculate the dot product. If it’s zero, congratulations! Your vectors are perpendicular. If it’s not zero, well, they’re hanging out at some other angle.
Let’s put it into action with an example. Suppose vector A is (2, 3) and vector B is (-3, 2). Their dot product is (2 -3) + (3 2) = -6 + 6 = 0. Boom! Perpendicular! You see it happen? It doesn’t matter if you’re working in two dimensions or three, the principle holds.