Divide by the distance of "b" instead of "a" from line ca?
Good catch! Yes, that's just a typo. You indeed want the ratio beta/h, where beta is the distance from x to the line ca, and h is the distance from b to the line ca (not a).
Divide by the distance of "b" instead of "a" from line ca?
Good catch! Yes, that's just a typo. You indeed want the ratio beta/h, where beta is the distance from x to the line ca, and h is the distance from b to the line ca (not a).