Question:medium

If \(f(x)=(x-1)^4+1 \quad \forall x\in[1,\infty)\). Statement–1 : \(f(x)=f^{-1}(x)\) has only two solutions. Statement–2 : \(f^{-1}(x+1)=f(x)\) has no solution.

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Equation \(f(x)=f^{-1}(x)\) corresponds to intersection points of the graph of \(f(x)\) with the line \(y=x\).
Updated On: Apr 9, 2026
  • Statement 1 and Statement 2 both are true
  • Statement 1 is false and Statement 2 is true
  • Statement 1 is true and Statement 2 is false
  • Statement 1 and Statement 2 both are false
Show Solution

The Correct Option is C

Solution and Explanation

Concept: If a function is one–one and increasing, the equation \(f(x)=f^{-1}(x)\) represents intersection points of the graph of \(f(x)\) with the line \(y=x\). Step 1: {Check monotonicity} \[ f(x)=(x-1)^4+1 \] \[ f'(x)=4(x-1)^3 \] For \(x\ge1\), \[ f'(x)\ge0 \] Thus \(f(x)\) is increasing. Step 2: {Solve \(f(x)=x\)} \[ (x-1)^4+1=x \] \[ (x-1)^4=x-1 \] Let \(y=x-1\). \[ y^4=y \] \[ y(y^3-1)=0 \] \[ y=0 \text{ or } y=1 \] Thus \[ x=1,\;2 \] Hence Statement–1 is true. Step 3: {Find inverse function} \[ y=(x-1)^4+1 \] \[ y-1=(x-1)^4 \] \[ x-1=(y-1)^{1/4} \] \[ f^{-1}(x)=(x-1)^{1/4}+1 \] Step 4: {Check Statement–2} \[ f^{-1}(x+1)=(x+1-1)^{1/4}+1 \] \[ =x^{1/4}+1 \] Equation becomes \[ x^{1/4}+1=(x-1)^4+1 \] \[ x^{1/4}=(x-1)^4 \] Graphically this equation has one solution, hence it is not true that it has no solution. Thus Statement–2 is false. Step 5: {Conclusion} Statement–1 is true and Statement–2 is false. \[ \boxed{\text{Option (3)}} \]
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