Update python/doc/usecases/use_case_stiffened_panel.rst

Co-authored-by: Michael Baudin <31351465+mbaudin47@users.noreply.github.com>

python/doc/usecases/use_case_stiffened_panel.rst

@@ -151,7 +151,7 @@ where:
 It leads to:
 
 .. math::
-  N_{xy}=q_1(1+q_c/q1)=\tau_{xy}t_s\left[1+\frac{1}{4}\frac{G_ct_c}{G_st_s}\frac{\left(2p(h-2h_0)-h_c(f_1-f_2)\right)}{h_0\ell}\right]
+  N_{xy}=q_1(1+q_c/q1) = \tau_{xy}t_s \left(1 + \frac{1}{4}\frac{G_ct_c}{G_st_s} \frac{\left(2p(h-2h_0) - h_c(f_1-f_2)\right)}{h_0\ell}\right)
 
 and finally, :math:`(N_{xy})_{cr}` is given by: