Determine the zeros of the function f(x) = x^2 - 7x - 8?

I would do it by graphing the function, e.g., y = x^2 – 7x – 8 on a graphing calculator or a graphing program like the Mac OS X Grapher. At first I could only see the curve cross the 0 line at –1, but then I zoomed out a little and saw that after dipping into the negative quadrants, it turns around and crosses the 0 line at 8. Then it's pretty clear that it goes off into infinity, so there shouldn't be any more zeroes.