Atriangle has two congruent sides that measure 8.7 cm and 12.3 cm. which could be the measure of the third side

Option C. 15 cm

Step-by-step 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

step-by-step explanation:

ok so im not 100% sure but you would start by adding 5.1t and 1.9t beacuse they have the same variable. that is 7t.   then add -3.6 + 1.2 which is -2.4

so then keep that as -2.4 + 7t. i apologize if this is incorrect. best luck on your test < 3