FUNCTIONS 1A

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).