Formulas For Inverse

Inverse Formulas and Definitions for Inverse:-

Inverse functions gives lots of troubles so here’s a swift run down of what an inverse function is, and how to find it.

  • For a function to have an inverse, the function has to be 1 to 1.  That means every output only has one input.

Inverse Formulas Example-

f(x) = 3x -2 and g(x) = \frac{x}{3} \ +  \frac{2}{3} \  

(f∘g)(x)= (g∘f)(x) = x

  • The first case is really,

  • The second case is really,


  • A function is called one-to-one if no two values of x produce the same y. Mathematically this is the same as saying
    f(x1)\neq f(x2)  whenever x1 \neq x2
  • Inverse functions are one to one functions f(x) and g(x) if
    (f∘g)(x) = x AND (g∘f)(x) = x, then we can say f(x) and g(x) are inverse to each other.
  • g(x) is inverse of f(x) and denoted by
    g(x)= f-1 (x)
  • Like wise f(x) is the inverse of g(x) are denoted by
    f(x)= g-1 (x)

For the two functions that we started off this section with we could write either of the following two sets of notation.
f(x) = 3x -2                  f-1 (x) = \frac{x}{3} \  \frac{2}{3} \

g(x) =  \frac{x}{3} \  \frac{2}{3} \              g-1 (x) = 3x-2

Inverse Formulas with solved

For Example-

Question 1.

Given f(x)  3x -2 find f-1 (x)


we’ll first replace f(x) with y
y= 3x-2
Next, replace x with y and all y with x.
x = 3y -2
x + 2 = 3y
 \frac{1}{3} \ (x+2) =y
 \frac{x}{3} \  \frac{2}{3} \ = y
Finally, replace y with f-1 (x)
f-1 (x) =  \frac{x}{3} \  \frac{2}{3} \

f∘f-1 (x) = f[f-1 (x)
= f[  \frac{x}{3} \  \frac{2}{3} \ ]
= 3 (  \frac{x}{3} \  \frac{2}{3} \ ) – 2
= x+2 – 2

Read Also: Tips and Tricks to solve Inverse question 

formulas for inverse

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