For what values of y does the following equation have no solutions for x?
xy+5y+4x+20=1
Clearly we'll have an equation of the form $ax+b=ax+c$. So $y=-4$, so $-4x+4x=1$, impossible.
Ans: $\boxed{-4}$.
Or, you could factor:
(x+5)(y+4)=1
When y = -4, the left-hand side will always equal zero, so y=−4 is the solution.
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