As can be seen from the above, in triangle and triangle, angular bed equals angle CFD equals 90 degrees, ED equals FD, BD equals CD, so these two triangles are congruent, so BD equals CF..
Note: When proving congruence, it must be stated that angle AED equals angle AFD equals 90 degrees, and angle bed equals angle CFD equals 90 degrees, otherwise congruence cannot be stated, because two line segments BD (or CD) can be drawn when the angle bed is acute.
In fact, you don't have to follow theorems and formulas!
College entrance examination questions can never be solved by pure theorems. It is most important to prove that your method is correct in your own way!
As for the corner, I don't remember it clearly! But you should pay attention, you have to prove that congruent triangles is a right triangle! Very special
I don't understand what you wrote, but if there are no conditions, your first sentence must be wrong!
Think about it, in a triangle, if two corresponding angles are equal, does it mean that three angles are equal, and three angles are equal to prove that two triangles are similar, because the corresponding hypotenuses are equal, can you prove congruence?
8. Because AD is perpendicular to CB and DB is perpendicular to CB.
So DBC angle = ACB angle =90 degrees.
In RT triangle ABC and RT triangle DCB
CB=BC
AB=DC
So consistent
So the angles are equal.
10。 Congruences (SAS) with the same vertex angle and the same two sides are then parallel through inner angles.
1 1。 Because FB=CE
So FB
FC=CE
Football club
So BC=EF
Because the parallel angles are equal.
Get congruence, so get edge equality.
Angle CBD = BDA；; ; So BF = df, af = cf in the right triangle CDF, CD=3, cf.
DF = 9； And df-cf = 9；; (CF
DF)*(DF-CF)= 9； Then df-cf =1; Solvable: DF=5, cf = 4；; Then the BDF area of the triangle =DF*AB/2=5*3/2=7.5.