# Need help about functions..!

• July 25th 2012, 05:51 AM
subhan2010
Need help about functions..!
Hi all(Hi)(Hi), can someone please give description about the use of composite and inverse functions with examples...? any help will be appreciated (Clapping)
• July 25th 2012, 02:49 PM
pickslides
Re: Need help about functions..!
I like to think of composit functions as one function inside another.

Consider $f(x)= x^2$ and $g(x) = \cos x$ then $f(g(x)) = g(x)^2 = (\cos x)^2$ is a composite function

For an inverse function, think about what the inverse of an operation is. If I square something the inverse operation is a square root. Therefore when thinking about functions i.e. $f(x) =x^2$ then the inverse is $f^{-1}(x) = \sqrt{x}$
• July 25th 2012, 05:17 PM
HallsofIvy
Re: Need help about functions..!
"Square" and "square root" are not good examples here. For example, if x= -2, then $x^2= 4$ and then $\sqrt{4}= 2$, not -2. That's because $f(x)= x^2$ is not "one-to-one"- both $2^2$ and $(-2)^2$ give four- so it does not have a true "inverse". A better example would be "cube" and "cube root". For any real number x, $\sqrt[3]{x^3}= \left(\sqrt[3]{2}\right)^3$.
• July 25th 2012, 05:44 PM
pickslides
Re: Need help about functions..!
Thanks HOI, a good point you raise.

Inverse functions only exist when a function is one to one. My example was not entirely correct, although should give you a taste of what it's all about.