BD = AC Given. BD cuts AC in half. That's what bisectors do.
BD = BD Reflexive property of a line (it is always equal to itself).
<ADB = <ADC = 90o
DB is perpendicular to AC Given.
<ADB + <ADC = 180o The two are supplementary.
Each angle = 90o Perpendicular means that one line meets another at 90o
2x = 180
x = 90o
Since each of the enclosed angles = 90, two have two triangles congruent by SAS <<<< Answer