Choose d with external angle, a=30+45=75, so choose d.

Choose c, we don't know if this 70 degree is the vertex angle. If it is the vertex angle, then this angle is 35 degrees. If 70 degrees is the base angle and the top angle is 180- 140=40, this angle is 20, so choose C.

The idea of choosing C to solve this problem is that there are so many equilateral sides here, it is best to draw the relationship between these angles and ∠A, and then use the sum of the inner angles of the triangle as 180 to solve ∠A, ok, let ∠A=x, AD=DE, so AED=A=x, EBD = X. Bdc=x/2+x=3/2x In triangle ABC, there are x+3/2x+3/2x = 180 and x = 45, so C is selected.

Gao Wei? The root number is 3/2a, the area is 3/4a?

5 or root number 7, note that it is not necessarily the hypotenuse.

1, very simple, do the math yourself.

Let BD=x, in the triangle DB'C (B falls on the side of AC and is called B'), there is X? + 16=(8-x)？ , solve x=3.