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# Help!

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If $$f(x)=\frac{ax+b}{cx+d}, abcd\not=0$$ and $$f(f(x))=x$$ for all $$x$$ in the domain of $$f$$, what is the value of $$a+d$$?

Apr 5, 2020

### 1+0 Answers

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As seen by the example f(x) = (x + 1)/(-x + 1), a + d = 2.

Apr 5, 2020