diff --git a/uni/mmme/1026_maths_for_engineering/vectors.md b/uni/mmme/1026_maths_for_engineering/vectors.md index b8e8d17..e91ddf5 100755 --- a/uni/mmme/1026_maths_for_engineering/vectors.md +++ b/uni/mmme/1026_maths_for_engineering/vectors.md @@ -58,12 +58,14 @@ Let $k$, an arbitrary scalar and $\pmb a$, an arbitrary vector. - $k(\pmb a + \pmb b) = k\pmb a + k\pmb b$ - $(k_1 + k_2)\pmb a = k_1\pmb a + k_2\pmb a$ - $(k_1k_2)\pmb a = k_1(k_2\pmb a)$ -- + ### The Scalar Product (Inner Product, Dot Product) The scalar product of two vectors $\pmb a$ and $\pmb b$ is a scalar defined by -$$\pmb a \cdot \pmb b = |\pmb a||\pmb b|\cos\theta$$ +$$\pmb a \cdot \pmb b = |\pmb a||\pmb b|\cos\theta = a_1b_1 + a_2b_2 + a_3b_3$$ + +where $\pmb a = (a_1, a_2, a_3)$ and $\pmb b = (b_1, b_2, b_3)$ where $\theta$ is the angle between the two vectors (note that $\cos\theta = \cos(2\pi - \theta)$). This definition does not depend on a coordinate system. @@ -78,9 +80,6 @@ This definition does not depend on a coordinate system. ii. One or both of the vectorse are zero vectors - $\pmb a \cdot \pmb a = |\pmb a|^2 = a^2$ -- If $\pmb a = (a_1, a_2, a_3)$ and $\pmb b = (b_1, b_2, b_3)$ then - - $$\pmb a \cdot \pmb b = a_1b_1 + a_2b_2 + a_3b_3$$ The base vectors are said to be *orthonormal* when $\pmb i^2 = \pmb j^2 = \pmb k^2 = 1$ and $i\cdot j = i\cdot k = j\cdot k = 0$.