Using the geometry of tangents:
\[Length of tangent = r \sqrt{3}\]
Substitute $r = 5 \, cm$:
\[Length = 5 \sqrt{3} \, cm\]
The equation of a circle which touches the straight lines $x + y = 2$, $x - y = 2$ and also touches the circle $x^2 + y^2 = 1$ is: