Let `f(x)=(ax + b )/(cx+d)`. Then the `fof (x)=x`, provided that : `(a – InterviewSolution

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1.	Let `f(x)=(ax + b )/(cx+d)`. Then the `fof (x)=x`, provided that : `(a!=0, b!= 0, c!=0,d!=0)`A. `d=-a`B. `d=a`C. `a=b=1`D. `a=b=c=d=1,`
Answer» Correct Answer - A `fof(x)=(a[(ax+b)/(cx+d)]+b)/(c[(ax+b)/(cx+d)]+d)=x` `therefore" "(ac+dc)x^(2)+(bc+d^(2)-bc-a^(2))x-ab-bd=0` It is true for all real x, `therefore" "(ac+dc)x^(2)+(bc+d^(2)-bc-a^(2))x-ab-bd =0` `"so "a=-d`

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