fix formula

neps/nep-0488.md

@@ -668,7 +668,7 @@ The rule of encoding is consistent with zkcrypto[^53] and with implementation in
 
 #### Compressed points on twisted curve E'(Fp2)
 
-The points on the curve represent by affine coordinates: `(x: Fp2, y: Fp2)`. The elements from $E'(F_{p^2})$ in compressed form are encoded in `[u8; 96]` as *big-endian* encoded $x \in F_{p^2}$. The $y$  coordinate can be detected by the formula: $y = \pm \sqrt{x^3 + 4}$.
+The points on the curve represent by affine coordinates: `(x: Fp2, y: Fp2)`. The elements from $E'(F_{p^2})$ in compressed form are encoded in `[u8; 96]` as *big-endian* encoded $x \in F_{p^2}$. The $y$  coordinate can be detected by the formula: $y = \pm \sqrt{x^3 + 4(u + 1)}$.
 
 *The highest bit* should be set as 1. This bit indicates that point is encoded in compressed form.