The third question will be calculated tomorrow. It is too late. This kind of question is a test of your computing ability. Please point out any mistakes that may be made.

Modify it. When calculating the area later, the base of multiplication should be 2-t, which is too late and confusing. There may be some errors in the final result, so the author can do some calculations by himself. The idea is to take the middle X axis of the triangle PQB as the bottom, and the sum of the upper and lower heights is the entire height of the triangle PQB, so the final area is the length of the middle X axis multiplied by | Y 1-Y2 |, and then take half.