[LolWolf]

In this case, any linear model (with reasonable, minimizable loss, which could be, say convex) will learn the correct thing.

Here's a quick gist[0] doing it using least-squares, and learning it exactly (also, for B in the third row you may have intended 35 instead of 45?).

This simple regression model learns exactly the weights (-1, 1)—equivalently, it learns -A + B = C.

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[0] https://gist.github.com/guillean/6f3ff05fa99b2b377fcf309bdc4...