FUNCTIONS B3

 If F(x) = 5x + 10; Find F^-1(40).

 

Solution

 

HINT: F^-1(x) means inverse.

 

PROCEDURE:

Make x the subject and then interchange x and y variables.

 

Let y=F(x)

 

So,  y= 5x + 10

 

y – 10 = 5x

 

y – 10  = ¹5x

   5          ₁5

 

y – 10   = x

    5

 

x  =   y – 10     after rearranging

            5

 

F^-1(x) = x – 10     after interchanging x and y variables.

                5

Now we calculate F^-1(40) as hereunder;

 

F^-1(40) = 40 – 10     

                  5

F^-1(40) =  30      

                 5

F^-1(40) =  6      [after dividing 30 by 5]

               

Hence, F^-1(40) =  6     

                             

TRY THIS……………………………

 

If F(x) = 7x - 20; Find F^-1(6).