Answer:
? = 5
Step-by-step explanation:
Look at the picture.
ΔADC and ΔCDB are similar (AAA). Therefore corresponding sides are in proportion
[tex]\dfrac{15}{x}=\dfrac{x}{20-15}\\\\\dfrac{15}{x}=\dfrac{x}{5}[/tex]
cross multiply
[tex]x^2=(15)(5)\\\\x^2=75\to x=\sqrt{75}\\\\x=\sqrt{25\cdot5}\\\\x=\sqrt{25}\cdot\sqrt5\\\\x=5\sqrt5[/tex]
