Answer:
x = 6
Step-by-step explanation:
Look at the picture.
ΔADC and ΔCDB are similar (AA). Therefore the sides are in proportion:
[tex]\dfrac{AD}{DC}=\dfrac{DC}{DB}[/tex]
We have
[tex]AD=9,\ DC=x,\ DB=4[/tex]
Substitute:
[tex]\dfrac{9}{x}=\dfrac{x}{4}[/tex] cross multiply
[tex]x^2=(9)(4)\\\\x^2=36\to x=\sqrt{36}\\\\x=6[/tex]
