Update l30.md

fixed a few typos

book/05_globalenvironment/l30/l30.md

@@ -104,13 +104,13 @@ Now, let's consider the possible steady state solutions to Eq. {eq}`eq:diffusive
 
 ```{math}
 :label: eq:equilibrium_temperature_eq
-A(1+\cos{\frac{2y}{R_e}})+(B-C)-DT_e + C_a \kappa \frac{d ^2 T_e}{d y^2}=0.
+C(1+\cos{\frac{2y}{R_e}})+(D-A)-BT_e + C_a \kappa \frac{d ^2 T_e}{d y^2}=0.
 ```
 
 Since this is a second order ODE, we need two boundary conditions. One choice is to ensure that the heat flux vanishes at the poles which requires that
 
 ```{math}
-\frac{\partial T}{\partial y}= 0, \quad @ \quad y=-90^\circ, 90^\circ.
+\frac{dT}{dy}= 0, \quad @ \quad y=-90^\circ, 90^\circ.
 ```
 
 Based on this boundary condition and the form of Eq. {eq}`eq:equilibrium_temperature_eq`, we might guess that the solution will be of the form