GeminiHeat wrote:
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In triangle ABC, AD = BD = DC (see figure). What is x?
A. 4
B. 6
C. 8
D. 10
E. 12
Since, AD = BD = DC
We have 2 Isosceles triangles: BDC, BDA and 1 Equilateral triangle: ADC
In ADC: AD = DC
Angle DAC = Angle DCA = 60
So, Angle ADC = 60
Now, In BDC: BD = DC
Angle DCB = Angle DBC = 20
So, Angle BDC = 140
And, In BDA: BD = DA
Angle DBA = Angle DAB = x
Angle BDA = 360 - 140 - 60 = 160
i.e. 2x = 180 - 160 = 20
x = 10
Hence, option D