Answer:Given :

radius of circle A = 5 cm,

radius of circle B = 3cm,

distance between the centers of the two circles = 13 cm.

Let  

O

1

and

O

2

be the center of Circle A and Circle B, respectively, as shown in the diagram.

Length of common tangent  

X

Y

,

Construct line segment  

Z

O

2

, which is parallel to  

X

Y

By Pythagorean theorem, we know that

Z

O

2

=

√

O

1

O

2

2

−

O

1

Z

2

=

√

13

2

−

2

2

=

√

165

=

12.85

Hence, length of common tangent  

X

Y

=

Z

O

2

=

√

165

=

12.85

(2dp)