Known: as shown in the figure, EF is the median line of trapezoidal ABCD, AF bisector angle DAB verification: ad = 2ef There is no picture

Known: as shown in the figure, EF is the median line of trapezoidal ABCD, AF bisector angle DAB verification: ad = 2ef There is no picture

The graph should be DC / / AB, EF is the median line, AF bisector angle DAB
Proof: because EF is the median line
So EF / / AB, and de = EA
So EFA = fab
And because AF bisectors DAB
So EAF = fab
That is, EAF = EFA
Then EA = EF
And because EA = 1 / 2ad
And EF = 1 / 2ad
So ad = 2ef

As shown in the figure, in the known trapezoid ABCD, ab ‖ CD, ad = BC, median EF = 15cm, ∠ DAB = 60 ° and AC bisects ∠ DAB, then the perimeter of the trapezoid is______ cm．

∵ EF = 15cm, ∵ CD + AB = 2ef = 30cm, ad = CD ∵ AC bisection ∵ DAB, ∵ DAC = ∵ BAC, and ∵ BAC = ∵ DCA, ∵ Da = DC, passing through point C as CG ∥ ad, crossing AB to g, ∵ ad = BC, ∵ DAB = 60 degree, ∵ CGB = 60 degree, CG = ad = BC, ∵ CGB is equilateral triangle, ∵ CG = GB = ad, ∵ AB = 2CD ∵

In trapezoidal ABCD, DC is parallel to ab. if the angle d = 120 ° ad = DC, ab = AC, calculate the angle DCB

Angle DAC = angle DCA = 30 ° (DA = DC)
Angle DAB = 60 ° (DC parallel AB)
So the angle cab = 30 degrees
So the angle BCA = 75 ° (AC = AB)
So the angle DCB = 75 ° + 30 ° = 105 °

In the trapezoidal ABCD, DC parallel AB angle d = 120 degrees ad = DC AB = AC is called the degree of DCB

105 degrees
Angle d = 120 degrees, because DC is parallel to AB, so the angle DAB is 60 degrees
Connect AC
Because ad = DC, the angle DAC of triangle ACD is equal to the angle DCA is equal to 30 degrees
So the angle cab equals 30 degrees
Because in triangle ACB, AC = AB, angle ACB equals angle ABC equals 75 degrees
So the angle DCB is 105 degrees