Two circles with radii 10 cm and 6 cm have their centers 20 cm apart. What is the approximate length of their common external tangent?
Show answer & explanation
Correct answer: C
Explanation
Length of the common external tangent of two circles = √(d² − (R − r)²)
= √(20² − (10 − 6)²)
= √(400 − 16)
= √384
= 8√6
≈ 19.6 ≈ 20 cm