The lengths of two sides of a triangle are 8 cm and 11 cm. The length of the third side must be:
Answer: C
The triangle inequality theorem states that the sum of the lengths of any two sides of a triangle must be greater than the length of the third side.
Let the third side be x.
x + 8 > 11 => x > 3
8 + 11 > x => 19 > x
So, the length of the third side must be between 3 cm and 19 cm.