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c3 functions doubt

Hello, I don't understand this question (*question no 4) on here at all ?

http://www.london-oratory.org/maths/Solomon%20C3%20Worksheets/C3Edex/pdf_files/E3Qfun_H.pdf

pls can someone explain what is going on with k ?

Reply 1

bcrazy

Original post by laurawoods

An inverse only exists when function is defined over a domain so that it is one-to-one. At the moment if you were to draw the function then it would have 2 possible x-values for each y-value so being told the output will not allow you to find the input. However, if we restricted the domain (limited the x-values in the first place) so that each y-value has only one corresponding x-value then the inverse would exist.

The question in a) is how to choose these x-values (do a little sketch of the graph and think about the turning point)
You should be able to choose a value k so that you only allow x values that are greater than k.