If $a_i$ is the $i^{th}$ row of $A$, then you have that $$(a_ix)(b^Tx)=y_i$$ Which has the LHS as the product of two "numbers". It may help to expand this out to write in quadratic form.
If $a_i$ is the $i^{th}$ row of $A$, then you have that $$(a_ix)(b^Tx)=y_i$$ Which has the LHS as the product of two "numbers". It may help to expand this out to write in quadratic form.