Screenshot
This is "grapes". It is graph making software we used this time.(This graph is y=1/2x^2)
First of all we made trout. We wrote numbers horizontally and alphabet vertically.
I placed an eraser in accordance with it.
By the way, we used the "grapes" to make trout.
Place four mirrors on the parabola and look for the focus with the eraser shown there.
I tried to enlarge the parabola