In △ ABC, ∠ BCA = 90 degrees, D and E are the middle points on the sides of AC and ab respectively, f is on the extension line of BC, ∠ CDF = ∠ a It's a proof

Simple. Connect D and E. then De is the median line of triangle ABC. It is directly parallel to BC. This is a theorem

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1. In △ ABC, ∠ ACB = 90 °, De is the median line of △ ABC, point F is on the extension line of BC, and ∠ CDF = ∠ a
2. As shown in the figure, in the right triangle ABC, the quadrilateral efbh is a square, ab = 21cm, BC = 28cm, AC = 35cm, ED is perpendicular to AC, ed = 8.4cm, what is the area of the square efbh?
3. As shown in the figure, in the right triangle ABC, D is the middle of hypotenuse AB, ED is perpendicular to point D, BC intersects point E, ab = 20, AC = 12. Find the area of quadrilateral Adec
4. As shown in the figure, in the right triangle ABC, e is the intersection of the bisectors of two acute angles, ed ⊥ BC is D, EF ⊥ AC is F. can you explain that the quadrilateral cdef is a square?
5. As shown in the figure, the triangle ABC is a right triangle, and the quadrilateral befd is a square. Given that the lengths of AB and BC are 12 cm and 20 cm respectively, what is the square area?
6. Triangle ABC is a right triangle, quadrilateral ACDE, fgba are square, ab = 8 cm, BC = 6 cm, triangle AEF
7. As shown in the figure, the triangle ABC is a right triangle, the quadrilateral EDFC is a square, the sum of the areas of the two shadow triangles is 32 square centimeters, ad: DB = 4:1, find the length of AD
8. The perimeter sum of an equilateral triangle ABC and a square defg is 95 decimeters. AB: de = 1:4. What is the side length of an equilateral triangle
9. The circumference of circle O is equal to 4 π cm. Find the side length, side center distance and area of its inscribed regular triangle ABC
10. In triangle ABC, D and E are the midpoint of AB and AC respectively, then the area ratio of triangle ade to quadrilateral DEBC is ()
11. In the triangle ABC, ∠ ACB = 90 ° points D and E are the middle points of AC and ab respectively, point F is on the extension line of BC, tangent ∠ CDF = ∠ a, prove that decf is ‖ quadrilateral
12. If ad = 6 and BD = 5, the sum of areas of △ ADF and △ BDE can be obtained
13. In △ ABC, ∠ C = 90 °, D, e and F are points on edges AB, AC and BC respectively, and the quadrilateral decf is a square if ad = 7
14. Cdef is the inscribed square of RT triangle ABC, BC = 2, AC = 1, find the square cdef area
15. As shown in the figure, in RT △ ABC, the bisector of ∠ a = 90 °, the bisector of ∠ B intersects AC at e, the height ah on the side of intersecting BC is at D, DF / / BC intersects AC at F through D, and the verification is: AE = FC
16. RT triangle ABC, ∠ a = 90 °, bisector of ∠ B intersects AC at D, vertical line from a as BC intersects BD at e, and vertical line from D as DF, so aefd is proved to be diamond
17. As shown in the figure, in △ ABC, the bisector of ∠ a = 90 ° and ∠ B intersects AC at D, ah and DF are perpendicular to BC, h and F are perpendicular feet
18. As shown in the figure, in △ ABC, the bisector of ∠ a = 90 ° and ∠ B intersects AC at D, ah and DF are perpendicular to BC, h and F are perpendicular feet
19. As shown in the figure, in △ ABC, the bisector of ∠ a = 90 ° and ∠ B intersects AC at D, ah and DF are perpendicular to BC, h and F are perpendicular feet
20. What is the full English name of NBA, PRC, VOA, EQ and WTO