Answer:
√(209)
Step-by-step explanation:
Since <B is a right angle, AC is the hypotenuse and AB and BC are legs.
(AB)² + (BC)² = (AC)²
(4 mm)² + (BC)² = (15 mm)²
16 mm² + (BC)² = 225 mm²
(BC)² = 209 mm²
BC = √(209) mm
