Answer:
Option C. 15 cm
Explanation:
The correct question is
A triangle has two sides that measure 8.7 cm and 12.3 cm. Which could be the measure of the third side?
A. 2.6 cm
B. 3.6 cm
C. 15 cm
D. 21 cm
we know that
The Triangle Inequality Theorem states that the sum of any 2 sides of a triangle must be greater than the measure of the third side
Analyze two cases
Let
x ----> the length of the third side
First case
x+8.7 > 12.3
x>12.3-8.7
x> 3.6 cm
Second case
12.3+8.7 > x
21 > x
Rewrite
x < 21 cm