please help me, with full explanation!!!!

Answer:
9.54 cm
Step-by-step explanation:
In triangle ABD, AD is the hypotenuse (longest side)
We know that according to Pythagoras theorem,
a^2+b^2=c^2
In the figure, c (10cm) and a (5cm) is given. So,
(5)^2 + b^2 = 100
25+b^2 = 100
b^2 = 75
So b is √75 = 8.66
Therefore BD is 8.66 cm
Now even BDC is a triangle
In it, the hypotenuse is missing but we know the value of other sides
so, in Pythagorean theorem,
a=4 (CD)
b=8.66 (BD)
c=x
Therefore,
(4)^2 + (8.66)^2 = x^2
16+74.99= x^2
x^2 = 90.99
x= 9.54 cm
Hope this helps!