Judging from the meaning of the question, (1+x- 1) x/2
X 2
The solution is [-1+√ (1+4× 4024)]/2
∵ [- 1+√( 1+4×4024)]/2≈62.94; √4024≈63.44; x∈Z+
∴x=63
The page number of this book is (1+x)/2 = (1+63) × 63/2 = 2016.
The wrong number is 20 16-20 12=4.