How do you find the exact value of $tan(tan^-1(-4.2))$ ?

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Answer 1 · 2016-09-28T14:12:05

The value of given expression is $-4.2$

If a function $f(x)$ has its inverse function $f^-1(x)$ , then the value of:

$f(f^-1(a))$ or $f^-1(f(a))$ is $a$ .

In the given example $a=-4.2$

How do you find the exact value of tan(tan^-1(-4.2))tan(tan^-1(-4.2))?