Marin writes the functions m(x) = StartFraction 3 x Over x + 7 EndFraction and n(x) = StartFraction 7 x Over 3 minus x EndFraction. Which equation must be true for m(x) and n(x) to be inverse functions?
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The functions m(x) and n(x) are inverses of each other and this is shown by the equation in option B.
To find an inverse function of a function (x,y), the y and x are interchanged and the equation is then solved for y.
The functions are :
[tex]\rm m(x) = \dfrac{3x}{x+7}[/tex]
[tex]\rm n(x) = \dfrac{7x}{3-x}[/tex]
The inverse of the function m(x) will be determined to check if both the functions given are inverse of each other
Let m(x) = y
[tex]\rm y= \dfrac{3x}{x+7}\\\\\\On \; Interchanging \ ; x \;a nd\; y\\\\x = \dfrac{3y}{y+7}[/tex]
As n(x) is the inverse of m(x) ,
[tex]\rm y = n(x) = \dfrac{7x}{3-x}[/tex]
Equation 1 is
[tex]\rm x = \dfrac{3( \dfrac{7x}{3-x})}{\dfrac{7x}{3-x} +7}\\[/tex]
same goes for function n(x)
[tex]\rm x = \dfrac{7y}{3-y}\\\\\\Equation \; 2 \; is\\x = \dfrac{7( \dfrac{3x}{x+7})}{3 - (\dfrac{3x}{x+7})}[/tex]
From equation 1 and 2
[tex]\rm x = \dfrac{3( \dfrac{7x}{3-x})}{\dfrac{7x}{3-x} +7} = \dfrac{7( \dfrac{3x}{x+7})}{3 - (\dfrac{3x}{x+7})}[/tex]
Therefore, the correct option is B
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