It is known that D.E.F in △ ABC is respectively the midpoint of three sides, and the sum of the perimeter of △ ABC and △ DEF is equal to 18cm, then the perimeter of △ DEF is?

It is known that D.E.F in △ ABC is respectively the midpoint of three sides, and the sum of the perimeter of △ ABC and △ DEF is equal to 18cm, then the perimeter of △ DEF is?

Each edge of △ DEF is half of its corresponding △ ABC bottom edge, so its perimeter is also half of △ ABC,
The perimeter of △ def = 18cm / 3 = 6cm

1. It is known that △ ABC is all equal to △ def, and the circumference of △ ABC is 12, ab = 5, BC = 4, then DF = ()
2. As shown in the figure, if △ ABC is all equal to △ OBC, and ∠ o = 65 ° and ∠ C = 20 °, then ∠ oad = ()
I don't know how to upload pictures!

1、3
2. What about the picture
2、95°

When △ def ≌ △ ABC, ab = AC, and the circumference of △ ABC is 23cm, BC = 4cm, DF is equal to?

In △ ABC, ∵ AB = AC, BC = 4cm and perimeter is 23cm ∵ AB = AC = 1 / 2 (23-4) cm = 9.5cm. ∵ def ≌ ABC ≌ DF = AC = 19.5cm