Assertion :If both functions f(t) and g(t) are continuous on the closed interval [a,b], differentiable on the open interval (a,b) and g′(t) is not zero on that open interval, then there exists some c in (a,b) such that f′(c)g′(c)=f(b)−f(a)g(b)−g(a) Reason: If f(t) and g(t) are continuous and differntiable in [a,b], then there exists some c in (a,b) such that f′(c)=f(b)−f(a)b−a and g′(c)=g(b)−g(a)b−a from Lagrange's mean value theorm.