@@ -56,7 +56,7 @@ $$
\vec{a} \cdot \vec{b} =
(^{x_a} _{y_a})
\cdot
-(^{x_b} _{y_b}) = x_a*x_b + y_a*y_b
+(^{x_b} _{y_b}) = x_a * x_b + y_a * y_b
$$
- 3D：
