Final answer:
The constant of proportionality between the sides of the two triangles is 1:1:1.
Step-by-step explanation:
To find the constant of proportionality between the sides of the two triangles, we need to compare the corresponding sides. In the first triangle, the ratio of the lengths of the sides is 12:14:20. In the second triangle, the ratio of the lengths of the sides is 36:42:60. We can simplify these ratios by dividing each side length by a common factor. For example, we can divide all the side lengths in the first triangle by 2 to get a simplified ratio of 6:7:10. Similarly, we can divide all the side lengths in the second triangle by 6 to get a simplified ratio of 6:7:10. Therefore, the constant of proportionality between the sides of the two triangles is 1:1:1.