(2)c？ =a？ +bc=4 1

(3) a? =c？ -B? =400? a=20

(4)a=2？ b= 1.5

First, multiple-choice questions: 1, B 2, a.

2. Fill in the blanks: 3.13;

4、60;

5、5

6、49

Third, answer the question: 7. Solution: BD? =3? +4? =5 BD=5

CD？ =5? + 12? = 13 CD= 13

Extension: 8,

Note that two triangles under a diagonal square (such as the one with an area of 1) can be used to prove congruence.

Using Pythagorean theorem for one of the triangles, we can get

S 1+S2= 1

similar

S3+S4=3

Addition of two formulas

S1+S2+S3+S4 =1+3 = 4 (this question needs to be marked with capital letters and angles in the triangle you require).

I have done all these questions, and the answers are all right. Ask for adoption ~