Hello, JadeKiara!

What I have done is divide the pond into two triangles,

and calculated them separately using Heron's formula for the non-right-angle triangle

and the standard formula for the area of a triangle.

The surface of a fish pond has the shape shown in the diagram (attached).

How many goldfish can the pond support if each fish requires 0.3 mē surface area of water?

All measurements are in metres.

I keep getting an answer of 20 goldfish;

the textbook says that the answer is 17 goldfish. Code:

1
* - - *
| * *
| * _ *
2| * √5 *
| * * 5
|* *
* *
* *
4 * *
* *
*

The right triangle has area $\displaystyle 1.$

The oblique triangle has area $\displaystyle \sqrt{19}.$

. . The total area is: .$\displaystyle 1 + \sqrt{19} \;\approx\;5.359$ mē.

This will support $\displaystyle \frac{5.359}{0.3} \:=\:17.863... \;\approx\;17 $ goldfish.