Answer:
CD=9
Step-by-step explanation:
ΔABD=>
AD²=AB² + BD² [Pythagorean Theorem]
BD²= AD²-AB²
BD²=9²-3²
BD²=72
BD=√72=6√2....(1)
ΔBCD=>
CD²=BD²+BC²
CD²=(6√2)² + 3²
CD²=72+9
CD²=81
CD=√81
