diff --git a/docs/chapters/pointvectors/pointvectors.js b/docs/chapters/pointvectors/pointvectors.js
index b79e694f..42e78662 100644
--- a/docs/chapters/pointvectors/pointvectors.js
+++ b/docs/chapters/pointvectors/pointvectors.js
@@ -69,7 +69,7 @@ getQuadraticDerivative(t, points) {
 }
 
 getCubicDerivative(t, points) {
-    let mt = (1 - t), a = mt*mt, b = mt*t, c = t*t, d = [
+    let mt = (1 - t), a = mt*mt, b = 2*mt*t, c = t*t, d = [
         {
             x: 3 * (points[1].x - points[0].x),
             y: 3 * (points[1].y - points[0].y)
diff --git a/docs/images/chapters/pointvectors/b8285282b8a0ce28fc2cc0392e9b607a.png b/docs/images/chapters/pointvectors/b8285282b8a0ce28fc2cc0392e9b607a.png
new file mode 100644
index 00000000..817d0c45
Binary files /dev/null and b/docs/images/chapters/pointvectors/b8285282b8a0ce28fc2cc0392e9b607a.png differ
diff --git a/docs/images/chapters/pointvectors/d0b09bb338bd42d4164ced871d1f77ba.png b/docs/images/chapters/pointvectors/d0b09bb338bd42d4164ced871d1f77ba.png
new file mode 100644
index 00000000..403dac6d
Binary files /dev/null and b/docs/images/chapters/pointvectors/d0b09bb338bd42d4164ced871d1f77ba.png differ
diff --git a/docs/index.html b/docs/index.html
index 0ec3e8a1..c06c5f34 100644
--- a/docs/index.html
+++ b/docs/index.html
@@ -38,7 +38,7 @@
 		<meta property="og:locale" content="en-GB" />
 		<meta property="og:type" content="article" />
 		<meta property="og:published_time" content="2013-06-13T12:00:00+00:00" />
-		<meta property="og:updated_time" content="2020-11-27T19:12:46+00:00" />
+		<meta property="og:updated_time" content="2020-11-27T19:49:03+00:00" />
 		<meta property="og:author" content="Mike 'Pomax' Kamermans" />
 		<meta property="og:section" content="Bézier Curves" />
 		<meta property="og:tag" content="Bézier Curves" />
@@ -3240,7 +3240,7 @@ Bézier'(n,t) = ❯      \undersetbinomial term\underbrace\binomki  · \ \unders
 						>
 							<fallback-image>
 								<span class="view-source">Scripts are disabled. Showing fallback image.</span>
-								<img width="275px" height="275px" src="./images/chapters/pointvectors/f1b4e81d22f4c44d4618b0f55a1a88c5.png" loading="lazy" />
+								<img width="275px" height="275px" src="./images/chapters/pointvectors/d0b09bb338bd42d4164ced871d1f77ba.png" loading="lazy" />
 								<label>Quadratic Bézier tangents and normals</label>
 							</fallback-image></graphics-element
 						>
@@ -3253,7 +3253,7 @@ Bézier'(n,t) = ❯      \undersetbinomial term\underbrace\binomki  · \ \unders
 						>
 							<fallback-image>
 								<span class="view-source">Scripts are disabled. Showing fallback image.</span>
-								<img width="275px" height="275px" src="./images/chapters/pointvectors/5863bd013ad6594f63f8dfa51ff4adc0.png" loading="lazy" />
+								<img width="275px" height="275px" src="./images/chapters/pointvectors/b8285282b8a0ce28fc2cc0392e9b607a.png" loading="lazy" />
 								<label>Cubic Bézier tangents and normals</label>
 							</fallback-image></graphics-element
 						>
diff --git a/docs/ja-JP/index.html b/docs/ja-JP/index.html
index da259c46..9103502b 100644
--- a/docs/ja-JP/index.html
+++ b/docs/ja-JP/index.html
@@ -41,7 +41,7 @@
 		<meta property="og:locale" content="ja-JP" />
 		<meta property="og:type" content="article" />
 		<meta property="og:published_time" content="2013-06-13T12:00:00+00:00" />
-		<meta property="og:updated_time" content="2020-11-27T19:12:46+00:00" />
+		<meta property="og:updated_time" content="2020-11-27T19:49:03+00:00" />
 		<meta property="og:author" content="Mike 'Pomax' Kamermans" />
 		<meta property="og:section" content="Bézier Curves" />
 		<meta property="og:tag" content="Bézier Curves" />
@@ -3198,7 +3198,7 @@ Bézier'(n,t) = ❯      \undersetbinomial term\underbrace\binomki  · \ \unders
 						>
 							<fallback-image>
 								<span class="view-source">Scripts are disabled. Showing fallback image.</span>
-								<img width="275px" height="275px" src="./images/chapters/pointvectors/f1b4e81d22f4c44d4618b0f55a1a88c5.png" loading="lazy" />
+								<img width="275px" height="275px" src="./images/chapters/pointvectors/d0b09bb338bd42d4164ced871d1f77ba.png" loading="lazy" />
 								<label>Quadratic Bézier tangents and normals</label>
 							</fallback-image></graphics-element
 						>
@@ -3213,7 +3213,7 @@ Bézier'(n,t) = ❯      \undersetbinomial term\underbrace\binomki  · \ \unders
 						>
 							<fallback-image>
 								<span class="view-source">Scripts are disabled. Showing fallback image.</span>
-								<img width="275px" height="275px" src="./images/chapters/pointvectors/5863bd013ad6594f63f8dfa51ff4adc0.png" loading="lazy" />
+								<img width="275px" height="275px" src="./images/chapters/pointvectors/b8285282b8a0ce28fc2cc0392e9b607a.png" loading="lazy" />
 								<label>Cubic Bézier tangents and normals</label>
 							</fallback-image></graphics-element
 						>
diff --git a/docs/news/2020-09-18.html b/docs/news/2020-09-18.html
index a6f21eab..edea5753 100644
--- a/docs/news/2020-09-18.html
+++ b/docs/news/2020-09-18.html
@@ -33,8 +33,8 @@
 		<meta property="og:description" content="Rewriting the tech stack" />
 		<meta property="og:locale" content="en-GB" />
 		<meta property="og:type" content="article" />
-		<meta property="og:published_time" content="Fri Sep 18 2020 00:00:00 +00:00" />
-		<meta property="og:updated_time" content="Fri Nov 27 2020 19:12:47 +00:00" />
+		<meta property="og:published_time" content="Thu Sep 17 2020 17:00:00 +00:00" />
+		<meta property="og:updated_time" content="Fri Nov 27 2020 11:49:03 +00:00" />
 		<meta property="og:author" content="Mike 'Pomax' Kamermans" />
 		<meta property="og:section" content="Bézier Curves" />
 		<meta property="og:tag" content="Bézier Curves" />
diff --git a/docs/news/2020-11-22.html b/docs/news/2020-11-22.html
index 18992a4b..a4233f70 100644
--- a/docs/news/2020-11-22.html
+++ b/docs/news/2020-11-22.html
@@ -33,8 +33,8 @@
 		<meta property="og:description" content="Curve-circle intersections" />
 		<meta property="og:locale" content="en-GB" />
 		<meta property="og:type" content="article" />
-		<meta property="og:published_time" content="Sun Nov 22 2020 00:00:00 +00:00" />
-		<meta property="og:updated_time" content="Fri Nov 27 2020 19:12:47 +00:00" />
+		<meta property="og:published_time" content="Sat Nov 21 2020 16:00:00 +00:00" />
+		<meta property="og:updated_time" content="Fri Nov 27 2020 11:49:03 +00:00" />
 		<meta property="og:author" content="Mike 'Pomax' Kamermans" />
 		<meta property="og:section" content="Bézier Curves" />
 		<meta property="og:tag" content="Bézier Curves" />
diff --git a/docs/news/index.html b/docs/news/index.html
index 6a050512..6064c727 100644
--- a/docs/news/index.html
+++ b/docs/news/index.html
@@ -33,7 +33,7 @@
 		<meta property="og:description" content="" />
 		<meta property="og:locale" content="en-GB" />
 		<meta property="og:type" content="article" />
-		<meta property="og:published_time" content="Fri Nov 27 2020 19:12:47 GMT+0000 (Coordinated Universal Time)" />
+		<meta property="og:published_time" content="Fri Nov 27 2020 11:49:03 GMT-0800 (Pacific Standard Time)" />
 		<meta property="og:updated_time" content="" />
 		<meta property="og:author" content="Mike 'Pomax' Kamermans" />
 		<meta property="og:section" content="Bézier Curves" />
diff --git a/docs/news/rss.xml b/docs/news/rss.xml
index e47aa276..37878616 100644
--- a/docs/news/rss.xml
+++ b/docs/news/rss.xml
@@ -6,7 +6,7 @@
   <atom:link href="https://pomax.github.io/bezierinfo" rel="self"></atom:link>
   <description>News updates for the <a href="https://pomax.github.io/bezierinfo">primer on Bézier Curves</a> by Pomax</description>
   <language>en-GB</language>
-  <lastBuildDate>Fri Nov 27 2020 19:12:47 +00:00</lastBuildDate>
+  <lastBuildDate>Fri Nov 27 2020 11:49:03 +00:00</lastBuildDate>
   <image>
     <url>https://pomax.github.io/bezierinfo/images/og-image.png</url>
     <title>A Primer on Bézier Curves</title>
@@ -23,7 +23,7 @@
 &lt;p&gt;— &lt;a href=&quot;https://twitter.com/TheRealPomax&quot;&gt;Pomax&lt;/a&gt;&lt;/p&gt;
 
     </description>
-    <pubDate>Sun Nov 22 2020 00:00:00 +00:00</pubDate>
+    <pubDate>Sat Nov 21 2020 16:00:00 +00:00</pubDate>
     <guid>2020-11-22.html</guid>
   </item><item>
     <title>Rewriting the tech stack</title>
@@ -119,7 +119,7 @@ draw() {
 &lt;p&gt;— &lt;a href=&quot;https://twitter.com/TheRealPomax&quot;&gt;Pomax&lt;/a&gt;&lt;/p&gt;
 
     </description>
-    <pubDate>Fri Sep 18 2020 00:00:00 +00:00</pubDate>
+    <pubDate>Thu Sep 17 2020 17:00:00 +00:00</pubDate>
     <guid>2020-09-18.html</guid>
   </item>
 </channel>
diff --git a/docs/uk-UA/index.html b/docs/uk-UA/index.html
index d4dbb7a9..38902b20 100644
--- a/docs/uk-UA/index.html
+++ b/docs/uk-UA/index.html
@@ -39,7 +39,7 @@
 		<meta property="og:locale" content="uk-UA" />
 		<meta property="og:type" content="article" />
 		<meta property="og:published_time" content="2013-06-13T12:00:00+00:00" />
-		<meta property="og:updated_time" content="2020-11-27T19:12:46+00:00" />
+		<meta property="og:updated_time" content="2020-11-27T19:49:03+00:00" />
 		<meta property="og:author" content="Mike 'Pomax' Kamermans" />
 		<meta property="og:section" content="Bézier Curves" />
 		<meta property="og:tag" content="Bézier Curves" />
@@ -3333,7 +3333,7 @@ Bézier'(n,t) = ❯      \undersetbinomial term\underbrace\binomki  · \ \unders
 						>
 							<fallback-image>
 								<span class="view-source">Скрипти вимкнено. показує резервний.</span>
-								<img width="275px" height="275px" src="./images/chapters/pointvectors/f1b4e81d22f4c44d4618b0f55a1a88c5.png" loading="lazy" />
+								<img width="275px" height="275px" src="./images/chapters/pointvectors/d0b09bb338bd42d4164ced871d1f77ba.png" loading="lazy" />
 								<label>Quadratic Bézier tangents and normals</label>
 							</fallback-image></graphics-element
 						>
@@ -3348,7 +3348,7 @@ Bézier'(n,t) = ❯      \undersetbinomial term\underbrace\binomki  · \ \unders
 						>
 							<fallback-image>
 								<span class="view-source">Скрипти вимкнено. показує резервний.</span>
-								<img width="275px" height="275px" src="./images/chapters/pointvectors/5863bd013ad6594f63f8dfa51ff4adc0.png" loading="lazy" />
+								<img width="275px" height="275px" src="./images/chapters/pointvectors/b8285282b8a0ce28fc2cc0392e9b607a.png" loading="lazy" />
 								<label>Cubic Bézier tangents and normals</label>
 							</fallback-image></graphics-element
 						>
diff --git a/docs/zh-CN/index.html b/docs/zh-CN/index.html
index 828a9456..2a2c2044 100644
--- a/docs/zh-CN/index.html
+++ b/docs/zh-CN/index.html
@@ -41,7 +41,7 @@
 		<meta property="og:locale" content="zh-CN" />
 		<meta property="og:type" content="article" />
 		<meta property="og:published_time" content="2013-06-13T12:00:00+00:00" />
-		<meta property="og:updated_time" content="2020-11-27T19:12:46+00:00" />
+		<meta property="og:updated_time" content="2020-11-27T19:49:03+00:00" />
 		<meta property="og:author" content="Mike 'Pomax' Kamermans" />
 		<meta property="og:section" content="Bézier Curves" />
 		<meta property="og:tag" content="Bézier Curves" />
@@ -3174,7 +3174,7 @@ Bézier'(n,t) = ❯      \undersetbinomial term\underbrace\binomki  · \ \unders
 						>
 							<fallback-image>
 								<span class="view-source">Scripts are disabled. Showing fallback image.</span>
-								<img width="275px" height="275px" src="./images/chapters/pointvectors/f1b4e81d22f4c44d4618b0f55a1a88c5.png" loading="lazy" />
+								<img width="275px" height="275px" src="./images/chapters/pointvectors/d0b09bb338bd42d4164ced871d1f77ba.png" loading="lazy" />
 								<label>Quadratic Bézier tangents and normals</label>
 							</fallback-image></graphics-element
 						>
@@ -3189,7 +3189,7 @@ Bézier'(n,t) = ❯      \undersetbinomial term\underbrace\binomki  · \ \unders
 						>
 							<fallback-image>
 								<span class="view-source">Scripts are disabled. Showing fallback image.</span>
-								<img width="275px" height="275px" src="./images/chapters/pointvectors/5863bd013ad6594f63f8dfa51ff4adc0.png" loading="lazy" />
+								<img width="275px" height="275px" src="./images/chapters/pointvectors/b8285282b8a0ce28fc2cc0392e9b607a.png" loading="lazy" />
 								<label>Cubic Bézier tangents and normals</label>
 							</fallback-image></graphics-element
 						>