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Example: Verifying that f(x)=5x1f(x) = 5x - 1 and g(x)=x+15g(x) = \frac{x+1}{5} are Inverse Functions

To verify that the functions f(x)=5x1f(x) = 5x - 1 and g(x)=x+15g(x) = \frac{x+1}{5} are inverse functions, one must confirm that their composition in both directions yields the identity function, meaning g(f(x))=xg(f(x)) = x and f(g(x))=xf(g(x)) = x. First, evaluate g(f(x))g(f(x)) by substituting 5x15x - 1 for xx in the function gg, yielding g(5x1)=(5x1)+15g(5x - 1) = \frac{(5x - 1) + 1}{5}. Simplifying the numerator gives 5x5\frac{5x}{5}, which reduces to xx. Next, evaluate f(g(x))f(g(x)) by substituting x+15\frac{x+1}{5} for xx in the function ff, yielding f\left(\frac{x+1}{5} ight) = 5\left(\frac{x+1}{5} ight) - 1. The 55s cancel out, leaving x+11x + 1 - 1, which also simplifies to xx. Because both g(f(x))=xg(f(x)) = x and f(g(x))=xf(g(x)) = x are true, it is algebraically verified that the functions f(x)=5x1f(x) = 5x - 1 and g(x)=x+15g(x) = \frac{x+1}{5} are inverses of each other.

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Updated 2026-05-25

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