Zhang Yu, Ph.D., is the author of Lecture on Advanced Mathematics for Postgraduate Entrance Examination 18 and Classic on the Origin of Mathematics for Postgraduate Entrance Examination 1000. Representative Works: Lecture 18 of Advanced Mathematics for Postgraduate Entrance Examination, Lecture 9 of Zhang Yu's Linear Algebra, Lecture 9 of Probability Theory and Mathematical Statistics for Postgraduate Entrance Examination, Classic of Mathematics Sources for Postgraduate Entrance Examination 1000, Complete Solution of the True Mathematics Question for Postgraduate Entrance Examination by Zhang Yu, and 180 Closed Math Exercise for Zhang Yu.