I'm going to call and , then, assuming no error, we have the equation , with the aim to solve for .
Normally, what could be done is to premultiply both sides by , but we can't do that in this case because is not a square matrix. But we can CREATE a square matrix by premultiplying both sides by first. This gives the equation .
Now that is a square matrix, to solve this equation for we need to premultiply both sides by , giving
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