Answer:
The answer to your question is: BC = √65 or 8.05 u
Explanation:
Data
AD = 12 u
BD = 15 u
AC = 4 u
BC = ?
First calculate the length of AB using the pythagorean theorem
BD² = AB² + AD²
AB² = BD² - AD²
AB² = 15² - 12²
AB² = 225 - 144
AB² = 81
AB = 9 u
Now, use the pythagorean theorem to find BC
AB² = BC² + AC²
BC² = AB² - AC²
BC² = 9² - 4²
BC² = 81 - 16
BC² = 65
BC = √65 or 8.05 u