So angle DEF= angle AEF=90 degrees, and side AE= side de.
Common edge EF
So triangle DEF is congruent with triangle AEF (SAS)
So angle ADF= angle DAF
Because angle ADF= angle B+ angle BAD
Angle DAF= angle CAF+ angle DAC
AD is the bisector angle of angle a BAD= angle DAC.
So angle B= angle CAF
2 AD bisects angle BAC, so angle BAD = angle DAC.
CE is perpendicular to AD, so angle AOE= angle AOC.
So the triangle is congruent with the triangle Cao (Asa).
So EO side OC side
Divide CE vertically in a triangle
So the triangle DCE is an isosceles triangle.
Angle DEC= angle DCE
Because EF and BC are parallel
So angel ·CEF = angel ·DCE
So angle DEC= angle CEF EC divides the angle equally.
Work plan for mathematics training in the second grade of primary school
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