Thread:Harkypoop/@comment-5578690-20150427045306

[ [5(x+h) + 2] - [5x + 2] ]/h

[5x+5h+2 - 5x - 2]/h

gives 5h/h = 5

f'(1,5) - you only have one variable, this is confusing

additonal http://www.wolframalpha.com/  