Production Cost: Show that C(x) is increasing function

[lilcherbear]

The cost C per day in dollars, of producing x paris of eyeglasses is C(x)=0.2x^2+3x+1000. Show that C is an increasing function.

I know that it has to be changed over to a derivative which is .4x+3 but that is far as I get. Can someone help me in the direction I would take in solving this problem?

Thanks...
Cherie

 

[stapel]

Hint: What is the definition of an "increasing" function? :wink:

Eliz.