If f(x) = − 5, what is f(8.6)?

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F(x) = -5.

This function is independent of x.  There is no term associated with x on the function.

Therefore  f(8.6) = -5  still.

f(8.6) = -5.

From the options there is no answer.

OR

you can write f(x) = -5

                       f(x) = -5x⁰           because    x⁰ = 1.

                       f(8.6) = -5*8.6⁰ = -5 *1,          8.6⁰ = 1   
                                                                (Any non zero raised to power zero is 1)
                       f(8.6) = -5
 
                       NO ANSWER  from the options given.   

Polar coordinates is 8,9