(a) 3.4 cm
In triangle ABC, AB = 2.5 cm and BC = 6 cm.
The length of a side must be less than the sum of the other two sides.
Let the side AC be x cm.
i.e.,
In addition, the length of a side must be greater then the difference between the other two sides.
i.e.,
Hence, the limits for the value of x is .
Thus, the length of AC cannot be 3.4 cm