= ｢(f(x+h)/g(x+h)−f(x)/g(x))/h :h⨠0｣
= ｢(f(x+h)·g(x)−f(x)·g(x+h))/(g(x+h)·g(x))/h :h⨠0｣ ➊
= ｢(f(x+h)·g(x)−f(x)·g(x+h))/h/(g(x+h)·g(x)) :h⨠0｣
= ｢(f(x+h)·g(x)−f(x)·g(x+h))/h :h⨠0｣
· ｢1/(g(x+h)·g(x)) :h⨠0｣
= ｢((f(x+h)−f(x))·g(x)−f(x)·(g(x+h)−g(x)))/h :h⨠0｣ ➋
· ｢1/(g(x+h)·g(x)):h⨠0｣
= ｢((f(x+h)−f(x))/h·g(x)−f(x)·(g(x+h)−g(x))/h) :h⨠0｣ ➌
· ｢1/(g(x+h)·g(x)):h⨠0｣
= (｢(f(x+h)−f(x))/h:h⨠0｣·g(x)−f(x)·｢(g(x+h)−g(x))/h:h⨠0｣)
· ｢1/(g(x+h)·g(x)):h⨠0｣
= ((f(x)▽x)·g(x)−f(x)·(g(x)▽x))/(g(x))²
➊ f(x+h)/g(x+h)−f(x)/g(x)
= (f(x+h)·g(x)−f(x)·g(x+h))/(g(x+h)·g(x))
➋ f(x+h)·g(x)−f(x)·g(x+h)
= f(x+h)·g(x)−f(x)·g(x)+f(x)·g(x)−f(x)·g(x+h)
= f(x+h)·g(x)−f(x)·g(x)−(f(x)·g(x+h)−f(x)·g(x))
= (f(x+h)−f(x))·g(x)−f(x)·(g(x+h)−g(x))
➌ ((f(x+h)−f(x))·g(x)−f(x)·(g(x+h)−g(x)))/h
= (f(x+h)−f(x))/h·g(x)−f(x)·(g(x+h)−g(x))/h
