there are 2 pentagons

the small pentagon has a side that is 3cm while the side on the other larger pentagon is 8cm.

the small pentagon has a side x cm while the same side on the larger pentagon is 5cm.

would i set up a proportion 3/x = 8/5

I think it is right

You are correct if the two pentagons are similar.

You did not mention if they are.

Yes, to determine if there is a proportionality between the sides of the two pentagons, you can set up a proportion using the given information.

The small pentagon has a side of 3 cm, and the corresponding side on the larger pentagon is 8 cm. Let's call the unknown side of the small pentagon "x" cm, and the corresponding side on the larger pentagon "5" cm.

So, the proportion can be set up as:

3/x = 8/5

To solve for "x", you can cross-multiply:

5 * 3 = 8 * x

15 = 8x

Next, divide both sides of the equation by 8 to isolate "x":

15/8 = x

Therefore, the value of "x" is 15/8 or 1.875 cm.

So, the corresponding side on the small pentagon (x) is approximately 1.875 cm when the corresponding side on the larger pentagon is 5 cm.