Covid19 has spread globally. When the Covid-19 pandemic occurs, schools must be closed or partially opened, which affects teaching and learning. Educational innovations to deal with epidemics such as Covid-19 and other urgent epidemics are very important. However, some areas of mathematics are still incomplete today, making some mathematical problems difficult or impossible to solve. This makes current technical tools such as online calculators unable to solve certain mathematical problems. This will cause students to reduce their interest in using today's technological tools and hinder the promotion of effective mathematics learning. In order to solve the above problems, my research is to create new discoveries (new rules, new methods, theorems or diagrams) to supplement the information needed to complete certain areas of mathematics. New discoveries can make solving certain mathematical problems easier, more direct and more accurate. After that, I applied my new discovery Peter Chew rule and triangle diagram to the PCET calculator (AI Age Calculator, https: //youtu.be/9m7mc0UTsSw). The new discovery enables the PCET calculator to solve all the problems in the topic solution of triangle can be solved directly, easily and accurately by single rule. When the future epidemics such as Covid-19 occur in the future, it can effectively help mathematics learning, especially for students studying at home. 2nd edition has some updates like if 2 sides and a containing angle were given, the previous math portal would show an error when we used the math portal to find another angle. However, Math Portal has been able to solve this problem for now. Therefore, 2nd edition focuses on updating the latest information. For anyone who buys my book (by Peter Chew), if you send proof of purchase to peterchew06@hotmail.com, you can get free AI Age Calculator, Peter Chew Triangle Calculator App. Peter Chew Triangle Calculator App guide students to solve all solution of triangle problems directly, easily and accurately by a single rule. Peter Chew Triangle Calculator doesn't have some incorrect or incomplete answers. Incorrect or incomplete answers appear on some calculators, e.g. Wolfram alfa (Law of sine). Peter Chew Triangle Diagram Calculator is one of the features of PCET Calculator.