Answer:
The missing side is 8.5 cm long.
Explanation:
Use Pythagorean theorem (a² + b² = c²).
Invert the formula to find what we want to find.
c² - b² = a²
Substitute what we have into the formula.
9² - 3² = a²
81 - 9 = a²
72 = a²
√72 = a
a = 8.4852 cm
a = 8.5 cm
The missing side is 8.5 cm.