-
If two circles of radii 9 cm and 4 cm touch externally, then the length of a common tangent is
-
- 5 cm
- 7 cm
- 8 cm
- 12 cm
- 5 cm
Correct Option: D
As per the given in question , we draw a figure of two circles of radii 9 cm and 4 cm touch externally
OO' = r1 + r2 = 9 + 4 = 13 cm
∴ Common tangent = √(r1 + r2)² - (r1 - r2)²
Common tangent = √13² - (9 - 4)²
Common tangent = √13² - 5² = √169 - 25
Common tangent = √144 = 12 cm
