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September 20th, 2015, 10:09 AM  #1 
Member Joined: Jun 2014 From: Alberta Posts: 56 Thanks: 2  Use the Definition of a Derivative for f(x) = kx + b
I can't figure out how to do this. f'(x) = lim(as h goes to 0) (k(x+h) + b  (k(x) + b))/h I tried using a conjugate, and I really don't know what other trick to try without getting an indeterminate answer. 
September 20th, 2015, 11:00 AM  #2  
Math Team Joined: May 2013 From: The Astral plane Posts: 2,151 Thanks: 875 Math Focus: Wibbly wobbly timeywimey stuff.  Quote:
$\displaystyle f'(x) = \lim_{h \to 0} \frac{(k(x + h) + b)  (kx + b)}{h}$ $\displaystyle f'(x) = \lim_{h \to 0} \frac{(kx + kh + b)  (kx + b)}{h}$ $\displaystyle f'(x) = \lim_{h \to 0} \frac{kx + kh + b  kx  b}{h}$ Can you finish from here? Dan  
September 20th, 2015, 06:30 PM  #3  
Member Joined: Jun 2014 From: Alberta Posts: 56 Thanks: 2  Quote:
 

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