MHB Difference Quotient of f(x)=1/(x-3)

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The difference quotient for the function f(x) = 1/(x-3) is calculated using the formula (f(x+h) - f(x))/h. Substituting f(x) into the formula leads to f(x+h) = 1/((x+h)-3). After simplification, the difference quotient becomes (1/((x+h)-3) - 1/(x-3))/h. Common mistakes often arise during the simplification process, particularly in combining fractions. Correctly applying algebraic techniques is essential for obtaining the accurate difference quotient.
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Simply and find the difference quotient for f(x)= 1/(x-3)

I know the difference quotient formula is f(x+h)-f(x)/h but when I try solving it I keep getting it wrong.
 
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kendalgenevieve said:
Simply and find the difference quotient for f(x)= 1/(x-3)

I know the difference quotient formula is f(x+h)-f(x)/h but when I try solving it I keep getting it wrong.

Hi kendalgenevieve!

How is it wrong?
What did you get?
 
There are probably loads of proofs of this online, but I do not want to cheat. Here is my attempt: Convexity says that $$f(\lambda a + (1-\lambda)b) \leq \lambda f(a) + (1-\lambda) f(b)$$ $$f(b + \lambda(a-b)) \leq f(b) + \lambda (f(a) - f(b))$$ We know from the intermediate value theorem that there exists a ##c \in (b,a)## such that $$\frac{f(a) - f(b)}{a-b} = f'(c).$$ Hence $$f(b + \lambda(a-b)) \leq f(b) + \lambda (a - b) f'(c))$$ $$\frac{f(b + \lambda(a-b)) - f(b)}{\lambda(a-b)}...

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