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avatar+86 

If f(x) = 5x for al real values of x and f -1(k) = -3, then k = ?

I can't figure out the answer for this.

 Apr 13, 2018
edited by SurpriseMe  Apr 13, 2018
 #1
avatar+18362 
+3

Find the inverse.....solve for x

y=5^x

log y = x log 5

logy /log5 = x          now change the x's and y's

 

y= logx/log5 = f^-1(x)

 

f^-1(k) = -3 = log k/log5         k= .008

 Apr 14, 2018
edited by ElectricPavlov  Apr 14, 2018
 #2
avatar+7616 
+3

f-1(k)  =  -3       so....

 

k  =  f(-3)

                        And   f(-3)  =  5-3

k  =  5-3

 

k  =  1 / 53

 

k   =   1 / 125

 

k   =   0.008

 Apr 14, 2018

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