fix a typo.

modules/imgproc/include/opencv2/imgproc.hpp

@@ -1867,7 +1867,7 @@ until the center stays within a set threshold.
 @param corners Initial coordinates of the input corners and refined coordinates provided for
 output.
 @param winSize Half of the side length of the search window. For example, if winSize=Size(5,5) ,
-then a \f$5*2+1 \times 5*2+1 = 11 \times 11\f$ search window is used.
+then a \f$(5*2+1) \times (5*2+1) = 11 \times 11\f$ search window is used.
 @param zeroZone Half of the size of the dead region in the middle of the search zone over which
 the summation in the formula below is not done. It is used sometimes to avoid possible
 singularities of the autocorrelation matrix. The value of (-1,-1) indicates that there is no such