Answer:
The correct answer is 4√3
Step-by-step explanation:
Consider the triangle ABC.
BC = 12 units. ∠ B = 90°. Let ∠ C = α°.
Now let us consider the triangle BDC.
DC = 4 units. ∠ D = 90°. Let ∠ C = α°.
We find here the angle C is common between both the triangles.
∴ For ΔABC, cos α° =
= 
and for Δ BDC, cos α° = 
Now equating both the equations we get,
= 48
⇒ BC = 4√3
The length of BC is 4√3 units.