# What does this look like?

Calculus Level 4

Let $$f:\mathbb R\rightarrow \mathbb R \backslash \{ 3\}$$ be a function given by

$f(x+10)=\frac { f(x)-5 }{ f(x)-3 }$

then $$\displaystyle \int _{ 10 }^{ 20 }{ f(x)\ dx }$$ is equal to?

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