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re
collinearity
author
Andrew Lorimer
<andrew@lorimer.id.au>
Tue, 5 Feb 2019 23:24:10 +0000
(10:24 +1100)
committer
Andrew Lorimer
<andrew@lorimer.id.au>
Tue, 5 Feb 2019 23:24:10 +0000
(10:24 +1100)
spec/vectors.md
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diff --git
a/spec/vectors.md
b/spec/vectors.md
index 0b6ea2a591579df2297f0fbb2caefea27642e9e6..db6598373fc53fe2f011284825156c99d00539e8 100644
(file)
--- a/
spec/vectors.md
+++ b/
spec/vectors.md
@@
-139,6
+139,8
@@
Vector resolute of $\boldsymbol{a}$ in direction of $\boldsymbol{b}$ is magnitud
$$\boldsymbol{u}={{\boldsymbol{a}\cdot\boldsymbol{b}}\over |\boldsymbol{b}|^2}\boldsymbol{b}=\left({\boldsymbol{a}\cdot{\boldsymbol{b} \over |\boldsymbol{b}|}}\right)\left({\boldsymbol{b} \over |\boldsymbol{b}|}\right)=(\boldsymbol{a} \cdot \hat{\boldsymbol{b}})\hat{\boldsymbol{b}}$$
$$\boldsymbol{u}={{\boldsymbol{a}\cdot\boldsymbol{b}}\over |\boldsymbol{b}|^2}\boldsymbol{b}=\left({\boldsymbol{a}\cdot{\boldsymbol{b} \over |\boldsymbol{b}|}}\right)\left({\boldsymbol{b} \over |\boldsymbol{b}|}\right)=(\boldsymbol{a} \cdot \hat{\boldsymbol{b}})\hat{\boldsymbol{b}}$$
+Scalar resolute of $\vec{a}$ on $\vec{b} = |\vec{u}| = \vec{a} \cdot \hat{\vec{b}}$
+
## Vector proofs
**Concurrent lines -** $\ge$ 3 lines intersect at a single point
## Vector proofs
**Concurrent lines -** $\ge$ 3 lines intersect at a single point
@@
-175,3
+177,6
@@
$$\cos \alpha = {a_1 \over |\vec{a}|}, \quad \cos \beta = {a_2 \over |\vec{a}|},
**on CAS:** `angle([a b c], [1 0 0])` for angle between $a\vec{i} + b\vec{j} + c\vec{k}$ and $x$-axis
**on CAS:** `angle([a b c], [1 0 0])` for angle between $a\vec{i} + b\vec{j} + c\vec{k}$ and $x$-axis
+## Collinearity
+
+Points $A, B, C$ are collinear iff $\vec{AC}=m\vec{AB} \text{ where } m \ne 0$