add index rule for i^n in C

diff --git a/spec/complex.md b/spec/complex.md
index d0b662566a18554c97db9ae06b0ad0824d42fc52..58091702e2e7c0c81da39bdc7a968cd05be29f84 100755 (executable)
--- a/spec/complex.md
+++ b/spec/complex.md
@@ -53,6 +53,8 @@ Therefore..
 - $i^{4n+2} = -1$
 - $i^{4n+3} = -i$
 
+Divide by 4 and take remainder
+
 ### Multiplying complex expressions
 
 If $z_1 = a+bi$ and $z_2=c+di$, then
@@ -97,7 +99,7 @@ ${z_1 \over z_2} = {{(a+bi)(c-di)} \over {c^2+d^2}}$
 To solve $z^2+a^2=0$ (sum of two squares):
 
 $z^2+a^2=z^2-(ai)^2$
-              $=(z+ai)(z-ai)$ 
+              $=(z+ai)(z-ai)$
 
 ## Polar form