From 55440b433433679457193c6eef12e9a2df17c5c5 Mon Sep 17 00:00:00 2001
From: Andrew Lorimer <andrew@lorimer.id.au>
Date: Wed, 15 May 2019 14:06:32 +1000
Subject: [PATCH] [spec] start differential equations & verifying solutions

---
 spec/calculus.md | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/spec/calculus.md b/spec/calculus.md
index 9d9ed36..c6818d4 100644
--- a/spec/calculus.md
+++ b/spec/calculus.md
@@ -384,3 +384,15 @@ If $f$ is continuous on $[a, b]$, then
 $$\int^b_a f(x) \> dx = F(b) - F(a)$$
 
 where $F$ is any antiderivative of $f$
+
+## Differential equations
+
+One or more derivatives
+
+**Order** - highest power inside derivative  
+**Degree** - highest power of highest derivative  
+e.g. ${\left(dy^2 \over d^2 x\right)}^3$: order 2, degree 3
+
+### Verifying solutions
+
+Start with $y=\dots$, and differentiate. Substitute into original equation.
-- 
2.43.2