Advertisements
Advertisements
प्रश्न
Consider the function f : R+ → [-9 , ∞ ]given by f(x) = 5x2 + 6x - 9. Prove that f is invertible with f -1 (y) = `(sqrt(54 + 5y) -3)/5` [CBSE 2015]
Advertisements
उत्तर
We have ,
f (x) = 5x2+ 6x − 9
Let y = 5x2+ 6x − 9
` = 5 (x^2 + 6/5x - 9/5)`
` = 5(x^2 + 2 xx x xx 3/5 + 9 /25 - 9/25 - 9/5)`
`= (( x + 3/5)^2 - 9/25 - 9/25)`
`=(x+ 3/5)^2 - 9/5 - 9 `
`= 5 (x + 3/5)^2 - 54/5`
⇒ `y + 54/5 = 5 (x+3/5)^2`
⇒ `(5y + 54)/25 (x + 3/5)^2`
⇒ `sqrt (5y +54)/25 = x +3/5`
⇒ `x = sqrt (5y +54)/5 - 3/5`
⇒ `x = (sqrt (5y +54)-3)/5 `
Let g (y) =` (sqrt(5y +54) -3)/5`
Now,
fog (y) = f (g (y))
= f `((sqrt (5y+54)-3)/5)`
= 5 `((sqrt (5y+54)-3)/5)^2 + 6 ((sqrt (5y+54)-3)/5) = - 9 `
`= 5 ((5y + 54 +9 - 6 sqrt (5y +54))/25) + ((6 sqrt(5y + 54) -18)/5) -9`
`= (5y + 63 - 6 sqrt (5y + 54))/5 +(6 sqrt (5y + 54)- 18)/5 -9`
=` (5y + 63 - 18 - 45) /5`
= y
= IY, Identity function
Also, gof (x) = g (f(x))
= g (5x2 + 6x - 9 )
`= (sqrt(5(5x^2 + 6x - 9)+ 54)-3)/5`
`= (sqrt(25x^2 + 30x - 45 +54) -3)/5`
`=(sqrt(25 x^2 + 30x + 9) -3)/5`
`= (sqrt((5x + 3)^2) - 3)/5`
`= (5x +3 -3)/5`
= x
= IX , Identity function
So, f is invertible .
Also, `f^-1 (y) = g (y) = (sqrt(5y +54) -3)/5`
APPEARS IN
संबंधित प्रश्न
Let f : R → R be defined as f(x) = x4. Choose the correct answer.
Which of the following functions from A to B are one-one and onto ?
f3 = {(a, x), (b, x), (c, z), (d, z)} ; A = {a, b, c, d,}, B = {x, y, z}.
Classify the following function as injection, surjection or bijection : f : N → N given by f(x) = x3
Classify the following function as injection, surjection or bijection :
f : R → R, defined by f(x) = sinx
If A = {1, 2, 3}, show that a onto function f : A → A must be one-one.
Let f : N → N be defined by
`f(n) = { (n+ 1, if n is odd),( n-1 , if n is even):}`
Show that f is a bijection.
[CBSE 2012, NCERT]
Give examples of two functions f : N → Z and g : Z → Z, such that gof is injective but gis not injective.
Find fog and gof if : f (x) = ex g(x) = loge x .
Find fog and gof if : f (x) = x+1, g (x) = sin x .
If f(x) = |x|, prove that fof = f.
State with reason whether the following functions have inverse :
f : {1, 2, 3, 4} → {10} with f = {(1, 10), (2, 10), (3, 10), (4, 10)}
State with reason whether the following functions have inverse :
g : {5, 6, 7, 8} → {1, 2, 3, 4} with g = {(5, 4), (6, 3), (7, 4), (8, 2)}
Let A = {1, 2, 3, 4}; B = {3, 5, 7, 9}; C = {7, 23, 47, 79} and f : A → B, g : B → C be defined as f(x) = 2x + 1 and g(x) = x2 − 2. Express (gof)−1 and f−1 og−1 as the sets of ordered pairs and verify that (gof)−1 = f−1 og−1.
Consider f : R → R+ → [4, ∞) given by f(x) = x2 + 4. Show that f is invertible with inverse f−1 of f given by f−1 `(x)= sqrt (x-4)` where R+ is the set of all non-negative real numbers.
A function f : R → R is defined as f(x) = x3 + 4. Is it a bijection or not? In case it is a bijection, find f−1 (3).
If f : R → (0, 2) defined by `f (x) =(e^x - e^(x))/(e^x +e^(-x))+1`is invertible , find f-1.
If f : A → A, g : A → A are two bijections, then prove that fog is an injection ?
Which one of the following graphs represents a function?
If A = {a, b, c} and B = {−2, −1, 0, 1, 2}, write the total number of one-one functions from A to B.
Let \[f : \left( - \frac{\pi}{2}, \frac{\pi}{2} \right) \to R\] be a function defined by f(x) = cos [x]. Write range (f).
Which one the following relations on A = {1, 2, 3} is a function?
f = {(1, 3), (2, 3), (3, 2)}, g = {(1, 2), (1, 3), (3, 1)} [NCERT EXEMPLAR]
Let
f : R → R be given by
\[f\left( x \right) = \left[ x^2 \right] + \left[ x + 1 \right] - 3\]
where [x] denotes the greatest integer less than or equal to x. Then, f(x) is
(d) one-one and onto
The function \[f : [0, \infty ) \to \text {R given by } f\left( x \right) = \frac{x}{x + 1} is\]
If a function\[f : [2, \infty )\text{ to B defined by f}\left( x \right) = x^2 - 4x + 5\] is a bijection, then B =
The function f : [-1/2, 1/2, 1/2] → [-π /2,π/2], defined by f (x) = `sin^-1` (3x - `4x^3`), is
Let A = ℝ − {3}, B = ℝ − {1}. Let f : A → B be defined by \[f\left( x \right) = \frac{x - 2}{x - 3}, \forall x \in A\] Show that f is bijective. Also, find
(i) x, if f−1(x) = 4
(ii) f−1(7)
If A = {a, b, c, d} and f = {a, b), (b, d), (c, a), (d, c)}, show that f is one-one from A onto A. Find f–1
Using the definition, prove that the function f: A→ B is invertible if and only if f is both one-one and onto
Let f: R → R be defined by f(x) = `1/x` ∀ x ∈ R. Then f is ______.
The function f: R → R defined as f(x) = x3 is:
Given a function If as f(x) = 5x + 4, x ∈ R. If g : R → R is inverse of function ‘f then
Students of Grade 9, planned to plant saplings along straight lines, parallel to each other to one side of the playground ensuring that they had enough play area. Let us assume that they planted one of the rows of the saplings along the line y = x − 4. Let L be the set of all lines which are parallel on the ground and R be a relation on L.
Answer the following using the above information.
- The function f: R → R defined by f(x) = x − 4 is ____________.
Raji visited the Exhibition along with her family. The Exhibition had a huge swing, which attracted many children. Raji found that the swing traced the path of a Parabola as given by y = x2.
Answer the following questions using the above information.
- The function f: Z → Z defined by f(x) = x2 is ____________.
Consider a set containing function A= {cos–1cosx, sin(sin–1x), sinx((sinx)2 – 1), etan{x}, `e^(|cosx| + |sinx|)`, sin(tan(cosx)), sin(tanx)}. B, C, D, are subsets of A, such that B contains periodic functions, C contains even functions, D contains odd functions then the value of n(B ∩ C) + n(B ∩ D) is ______ where {.} denotes the fractional part of functions)
If f: [0, 1]→[0, 1] is defined by f(x) = `(x + 1)/4` and `d/(dx) underbrace(((fofof......of)(x)))_("n" "times")""|_(x = 1/2) = 1/"m"^"n"`, m ∈ N, then the value of 'm' is ______.
Let f(x) be a polynomial function of degree 6 such that `d/dx (f(x))` = (x – 1)3 (x – 3)2, then
Assertion (A): f(x) has a minimum at x = 1.
Reason (R): When `d/dx (f(x)) < 0, ∀ x ∈ (a - h, a)` and `d/dx (f(x)) > 0, ∀ x ∈ (a, a + h)`; where 'h' is an infinitesimally small positive quantity, then f(x) has a minimum at x = a, provided f(x) is continuous at x = a.
