If f∘g(x)= and g∘f(x)=∣sinx∣, then
If f∘g(x)= √x and g∘f(x)=∣sinx∣, then
- A.
f and g cannot be determined
- B.
f(x)=sin x
- C.
f(x)=x2, g(x)=sin x
- D.
f(x)=(x),g(x)=√x
Attempted by 68 students.
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Correct answer: A
(a)
Given Conditions:
1.) (f ∘ g) (x) = √x
⇒ f(g(x)) = √x (Equation 1)
2.) (g ∘ f) (x) = ∣sin x∣
⇒g(f(x)) = ∣sin x∣ (Equation 2)
Checking the Given Options:
Option (D): f(x)=x, g(x)=x
-> Compute f(g(x)) : f(g(x)) = f(√x) = √x
o Satisfies f ∘ g(x)= x (Equation 1)
-> Compute g(f(x)): g(f(x)) = g(x) = √x
o This must equal ∣sin x∣, but x ≠ ∣sin x∣ in general.
o Does not satisfy Equation 2.
Conclusion: Incorrect.
Option (B): f(x)=sin x
->Compute f(g(x)): f(g(x)) = sin(g(x))
o For this to be √x , we would need sin(g(x)) = x, which isn't a general identity.
o Does not satisfy Equation 1.
->Compute g(f(x)): g(f(x)) = g(sin x)
o If g(x)=∣x∣, then g(f(x)) = ∣sin x∣, which satisfies Equation 2.
But since f(g(x)) = sin(g(x)) ≠ x, this option is incorrect.
Option (C): f(x) = x2, g(x)=sin x
->Compute f(g(x)):
o f(g(x)) = f(sin x)=(sin x)2
o This must equal √x, but (sin x)2 does not match √x in general.
o Does not satisfy Equation 1.
-> Compute g(f(x)): g(f(x)) = g(x2) = sin(x2)
o This must equal ∣sin x∣, but sin(x2) ≠ ∣sin x∣ in general.
o Does not satisfy Equation 2.
Conclusion: Incorrect.
Option (A): f and g cannot be determined.
->Since none of the options satisfy both conditions simultaneously, we cannot determine explicit functions f(x) and g(x) from the given choices.
Correct Answer: (A) f and g cannot be determined.