I got a math problem that looks like this. 

Find the point P in the first quadrant on the curve y=x^3 such that
the slope of the line passing through P and (1,1) is 3.

I used substitution and the definition of slope to solve it. My answer
is (-2,-8) and the computer says it's incorrect. Anyone know the
correct answer and how to get there, so I can find my mistake.

(-2,-8) is not in the first quadrant (x>0, y>0).  This appears to be a
poorly conceived trick question or something because (hint
approaching) the only P that kind of works doesn't even form a line
with (1,1).

Yep.  Trick question or bad question.
The polynomial and the line at (1,1) only intersect at two points,
first and third quadant.  Maxmouse found the third quadrant point
(that should count for something).  The first quadrant point is (1,1),
not a valid choice when defining a line.

Funny, the polynomial for the intersection has three roots, but two of
them are the same.

This was a fun problem to solve at the end of a hard day.  Brushed up
on some  algebra I had forgotten.