Fix capitalization of word Cartesian.

07/README.md

@@ -90,7 +90,7 @@ Before going forward, try the following exercises:
 
 ### Circles
 
-It's easy to draw squares on grid paper and rectangles on cartesian coordinates, but circles require another approach, especially since we need a "per-pixel" algorithm. One solution is to *re-map* the spatial coordinates so that we can use a [`step()`](../glossary/?search=step) function to draw a circle.
+It's easy to draw squares on grid paper and rectangles on Cartesian coordinates, but circles require another approach, especially since we need a "per-pixel" algorithm. One solution is to *re-map* the spatial coordinates so that we can use a [`step()`](../glossary/?search=step) function to draw a circle.
 
 How? Let's start by going back to math class and the grid paper, where we opened a compass to the radius of a circle, pressed one of the compass points at the center of the circle and then traced the edge of the circle with a simple spin.
 
@@ -184,7 +184,7 @@ Finish uncommenting *lines 27 to 29* one by one to understand the different uses
 
 ![Robert Mangold - Untitled (2008)](mangold.jpg)
 
-In the chapter about color we map the cartesian coordinates to polar coordinates by calculating the *radius* and *angles* of each pixel with the following formula:
+In the chapter about color we map the Cartesian coordinates to polar coordinates by calculating the *radius* and *angles* of each pixel with the following formula:
 
 ```glsl
 vec2 pos = vec2(0.5)-st;
@@ -196,7 +196,7 @@ We use part of this formula at the beginning of the chapter to draw a circle. We
 
 This technique is a little restrictive but very simple. It consists of changing the radius of a circle depending on the angle to achieve different shapes. How does the modulation work? Yes, using shaping functions!
 
-Below you will find the same functions in the cartesian graph and in a polar coordinates shader example (between *lines 21 and 25*). Uncomment the functions one-by-one, paying attention the relationship between one coordinate system and the other.
+Below you will find the same functions in the Cartesian graph and in a polar coordinates shader example (between *lines 21 and 25*). Uncomment the functions one-by-one, paying attention the relationship between one coordinate system and the other.
 
 <div class="simpleFunction" data="y = cos(x*3.);
 //y = abs(cos(x*3.));