diff --git a/book/fem/shape.md b/book/fem/shape.md
index 62296a67091cad516a3a659d96a6b4a5b397579d..e58b1106af6a44a769963bbdbc1d5bd68dc6eebb 100644
--- a/book/fem/shape.md
+++ b/book/fem/shape.md
@@ -160,7 +160,7 @@ The 9-node quadrilateral element
 A popular alternative is one where the center node is removed, resulting in an 8-node quadrilateral element with the following shape function:
 
 $$
-N_i=a_i+b_ix+c_iy+d_ix^2+e_ixy+f_iy^2+g_ix^2y+h_ixy
+N_i=a_i+b_ix+c_iy+d_ix^2+e_ixy+f_iy^2+g_ix^2y+h_ixy^2
 $$