If f a + b + 1 - x = f x , for all x , where a and b are fixed positive real numbers, then 1 a + b ∫ a…

If fa+b+1-x=fx, for all x, where a and b are fixed positive real numbers, then 1a+babxfx+fx+1dx is equal to
  1. a-1b-1fx+1dx
  2. a-1b-1fxdx
  3. a+1b+1fxdx
  4. a+1b+1fx+1dx

Solution

I=1a+babxfx+fx+1dx      1
xa+b-x
I=1a+baba+b-xfa+b-x+a+b+1-xdx
I=1a+babaa+b-xfx+1+fxdx      2
 Keeping xx+1 in given relation
1+2
2I=abfx+1+fxdx
2I=abfx+1dx+abfxdx
abfa+b+1-xdx+abfxdx
2I=2abfxdx
I=abfxdx
Put x=t+1I=a-1b-1ft+1dt=a-1b-1fx+1dx

Asked in: JEE Main 2020 (07 Jan Shift 1)

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