Inverse Functions test
- Author:
- mathtasksproj, Carlos
- Topic:
- Functions
The definition of inverse functions.
An inverse function is a function such that and . In other words, given a function f(x), which has some operations(squaring, multiplying, adding..), the inverse function will perform the opposite operations of the original function(square root, dividing, subtracting...) in such a way that when evaluating or , the original value, x, will be obtained.
The graph below shows the function and two points: and . By adjusting the values of a, you can move the points A and B. Notice how they move along the graph: as A moves along , B moves along .
For example, when a=1, and . When we put the value 1 in, it returns , after that we put into and it returns to us 1, this process is the same as performing , and since the returned value is the original value, is the inverse function of
Using the graph of , and your knowledge of inverse functions, can you estimate the values of ? What about ?
Graphing the inverse
To have an inverse, a function must satisfy two requirements: be injective(one-to-one) and surjective(onto), i.e. it must be a bijection. The graph of the inverted function will always be the mirror image of the original function reflected about the y=x line.
In the graph below you can see this reflection in action. By adjusting the values of a, the point moves along the graph and traces the graph of the inverse. The same happens for and the points . You can click on the circles next to the functions/points to hide/show them.
The point draws the graph of a function as you change a, find and using the values of . Then, click on the empty box under the points and type in your function and inverse, see if they are reflected about the y=x line.
Non-bijective functions
It becomes clear why functions that are not bijections cannot have an inverse simply by analysing their graphs. The example below shows the graph of and its reflection along the y=x line. Why is the reflection not the inverse function of ? (tip: recall the vertical line test)