Update 1_complex_numbers.md Mistake in an example (8 instead of 4)

src/1_complex_numbers.md

@@ -71,7 +71,7 @@ Check this!
 
 !!! check "Example:"
     $$\begin{align} 
-    \frac{1 + 2{\rm i}}{1 - 2{\rm i}} &= \frac{(1 + 2{\rm i})(1 + 2{\rm i})}{1^2 + 2^2} = \frac{1+8{\rm i} -4}{5}\\
+    \frac{1 + 2{\rm i}}{1 - 2{\rm i}} &= \frac{(1 + 2{\rm i})(1 + 2{\rm i})}{1^2 + 2^2} = \frac{1+4{\rm i} -4}{5}\\
     & = -\frac{3}{5} + {\rm i} \frac{8}{5}
     \end{align}$$