Functions 2 Question 4

5. For xR0,1, let f1(x)=1x,f2(x)=1x and f3(x)=11x be three given functions. If a function, J(x) satisfies (f2Jf1)(x)=f3(x), then J(x) is equal to

(2019 Main, 9 Jan I)

(a) f2(x)

(b) f3(x)

(c) f1(x)

(d) 1xf3(x)

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Answer:

Correct Answer: 5. (b)

Solution:

  1. We have,

f1(x)=1x,f2(x)=1x and f3(x)=11x

Also, we have (f2J o f1)(x)=f3(x)

f2((Jof1)(x))=f3(x)f2(J(f1(x))=f3(x)1J(f1(x))=11x[f2(x)=1x and f3(x)=11x]1J1x=11x[f1(x)=1x]J1x=111x=1x11x=x1x

Now, put 1x=X, then

J(X)=1X11X=1X1=11X

J(X)=f3(X) or J(x)=f3(x)



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