Answer:
D
Step-by-step explanation:
The triangles CDA and ADB are similar, thus the ratios of corresponding sides are equal, that is
[tex]\frac{CD}{AD}[/tex] = [tex]\frac{DA}{DB}[/tex] , substitute values
[tex]\frac{13}{x}[/tex] = [tex]\frac{x}{3}[/tex] ( cross- multiply )
x² = 39 ( take square root of both sides )
x = [tex]\sqrt{39}[/tex] → D
