We have a point $P(1,7)$, get the equations of the 2 lines which have a distance of $5$ from point $P$. Both of the lines go through the origin.
So I used the formula $\dfrac{|ax+by-c|}{\sqrt{a^2+b^2}} = 5$
However, I only know $x, y$ and $c$. My teacher however, he said the $b$ must be $-1$. This I don't understand. Why $b = -1$? I know how to solve it once I fill in $-1$ for $b$, I just need some clarification:
Why $b=-1$?
I believe it has something to do with the fact that the lines go through the origin.
I posted a question about this problem about half a month ago, however, this is a different one and is only about the line in bold, not about the problem itself.