The triangle is formed by three line segments 4cm, 8cm and 2cm, then it should satisfy the inequality theorem.
Hence, let us check if the sum of two sides is greater than the third side.
4 + 8 > 2 ⇒ 12 > 2 ⇒ True
8 + 2 > 4 ⇒ 10 > 4 ⇒ True
4 + 2 > 8 ⇒ 6 > 8 ⇒ False
Therefore, the sides of the triangle do not satisfy the inequality theorem. So, we cannot construct a triangle with these three line-segments.