Question

Note: I am not looking for the entire answer to this question:

A trough is filled with a liquid density of 840 kg/m³

^{The ends are equalateral triangles with a side length of 8m and the vertex at the bottom.}

^{Find the hydrostatic force on one end of the trough.}

^{I am wondering why the length of our sample strip is 8 - 2x_i /Sqrt(3) . Or more specifically, how am I supposed to realize that we are subtracting our 2a from 8. Plugging in numbers I can see that it is true, but I would have never guessed that we needed to do that, any advice on what I should be looking for?}