Answer:
qr = 2a + 3b
Explanation:
First, we must calculate the measure of each side based on the perimeter. Since all three sides of an equilateral triangle are equal, we divide the perimeter by 3.
![(12a+18b)/(3)](https://img.qammunity.org/2019/formulas/mathematics/high-school/dcmdrr9pgw9cj41lbk1g6jeyb1mei3d988.png)
![(12a)/(3)+(18b)/(3)](https://img.qammunity.org/2019/formulas/mathematics/high-school/hvwrzdbqrkl8fnbor7ygq9y8hfnic8ehsa.png)
4a + 6b (measure of each side)
Being an equilateral triangle, any middle segment is half the length of any of its sides.
So, the value of qr is:
![qr = (4a+6b)/(2)\\qr = (4a)/(2) + (6b)/(2) \\qr = 2a + 3b](https://img.qammunity.org/2019/formulas/mathematics/high-school/9effkehzaw8g8l2gclvnvdhiosg6ewl05p.png)
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Hope this hepls!