PISA survey research revealed that Japanese high school students have difficulty using mathematics. Responding to those survey results and aiming at improving this situation, the Japanese Ministry of Education, Culture, Sports, Science and Technology created a new subject designated as "Application of Mathematics" in which mathematics is developed with close involvement in culture. The design of the subject "Application of Mathematics" is based on two fundamental pillars: "human activity and mathematics", and "mathematical considerations for social life". In this talk, the author wants to add a new perspective: "Application of Mathematics to Mathematics". Accordingly, the talk will present some examples from WASAN problems of this concept using Computer Algebra Systems (CAS), such as Mathematica, Maple, Maxima, Scilab and R, and TeX documents used as classroom materials through KETpic. The talk encompasses the author's practice in the teacher-training course and high school classes with CAS. This approach is particularly effective for students in the field of geometry.