Answer: Missing parts are,
In first blank,
,
In second blank, SAS postulate
In third blank, CPCTC postulate
Step-by-step explanation:
Since, Here D is the mid point on the line segment AC.
And BD is a perpendicular to the line AC.
Therefore, In triangles ADB and CDB ( shown in figure)
AD\cong DC ( By the definition of mid point)
( right angles )
( reflexive)
Thus, By SAS ( side angle side )postulate,

So, by CPCTC( Corresponding parts of congruent triangles are congruent)

Now, By definition of congruent segment,
AB=CB
By definition of equidistant,
B is equally far from both A and C.