So ∠ bed = ∠ c = 90.
And BD shares ∠ABC, so ∠CBD=∠EBD.
And because BD=BD.
So △CBD is equal to △EBD.
So CD=DE=3
That is, the distance from point D to AB is 3.
10) Let the perpendicular line of AB intersect with AB at point E and with AC at point D..
Therefore, AE = be, ∠ aed = ∠ bed = 90.
And DE=DE
So △ADE is equal to △BDE.
So AD=BD=7cm.
And AC= 10cm.
So CD= 10-7=3cm.
Judging from these two questions, you are not very skilled in proving the congruence of triangles.