Though I donot know the right soln. I think Propensity is wrong.Propensity's staement are not general. two roots mean there is a maxima and a minima...how abt if two roots are identical? one root means there is one point of inflection...is perhaps true. and no root means there is no mamima, minima...wat abt 2+0.1sin(60t)? this has no root but has max n minima....... i might be wrong...as i m not a mathematics student.