Answer: K = 6
Explanation:
If you find the inverse of the inverse function, it will return back to initial function.
The inverse of r^-1 (x) will give r(x).
To find the inverse of r^-1(x), let it be equal to y. Interchange y and x for each other and make y the subject of formula. That is,
Y = 2x^2 - 14
Interchange y for x
X = 2y^2 - 14
2y^2 = x + 14
Y^2 = x/2 + 14/2
Square both side
Y = sqrt ( x/2 + 7 )
It is only when K = 6, that will can get the value above.