Answer:
Option (4)
Explanation:
From the picture attached,
It is given that ΔCBD is a right triangle.
Therefore, it will follow Pythagoras theorem which states that,
(Hypotenuse)² = (Leg 1)² + (Leg 2)²
(BC)² = BD² + CD²
a² = h² + x²
h² = a² - x²
Option (4) will be the correct option.