If $$AD = DB$$, $$DC =CB$$, and angle $$ABC = 90º$$ as shown above, then what is the value of $$xº$$?

Correct.
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Given that $$CB = CD$$,
> $$\displaystyle{\angle CBD = \angle CDB = \frac{180º - 100º}{2} = 40º}$$.
Given that angle $$ABC$$ is a right angle, $$\angle DBA = 90º - 40º = 50º$$. Since $$AD = DB$$, $$\angle DAB = \angle DBA$$. Hence, $$xº=50º$$.

Incorrect.
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Incorrect.
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Incorrect.
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Incorrect.
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$$40º$$

$$50º$$

$$65º$$

$$80º$$

$$100º$$