Multiply the matching components of the two vectors
Add the products together
For vectors a = (a1, a2, …, an) and b = (b1, b2, …, bn), use a · b = a1b1 + a2b2 + … + anbn
For 2D vectors, use a · b = axbx + ayby
For 3D vectors, use a · b = axbx + ayby + azbz
If the result is 0, the vectors are perpendicular