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Functions question

2021 · 24 Feb · Shift 2 · Q37
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Functions question

2021 · 24 Feb · Shift 2 · Q37

JEE MainMathematicsFunctionsNumerical+4 / −1
If a + α\alphaα= 1, b +β\betaβ= 2 and af(x)+αf(1x)=bx+βx,xe0af(x) + \alpha f\left( {{1 \over x}} \right) = bx + {\beta \over x},x e 0af(x)+αf(x1​)=bx+xβ​,xe0, then the value of the expression f(x)+f(1x)x+1x{{f(x) + f\left( {{1 \over x}} \right)} \over {x + {1 \over x}}}x+x1​f(x)+f(x1​)​ is ‾\underline{\hspace{2cm}}​.
Numerical answer
View written solutionFree

Correct answer: 2

  1. We are given a+α=1,b+β=2a+\alpha=1,\qquad b+\beta=2a+α=1,b+β=2 and af(x)+αf(1x)=bx+βx,x≠0.a f(x)+\alpha f\left(\frac1x\right)=bx+\frac{\beta}{x}, \qquad x\ne 0.af(x)+αf(x1​)=bx+xβ​,x=0.

We need to find f(x)+f(1x)x+1x.\frac{f(x)+f\left(\frac1x\right)}{x+\frac1x}.x+x1​f(x)+f(x1​)​.

  1. Write the given relation again, and then replace xxx by 1x\dfrac1xx1​.

From the given equation: af(x)+αf(1x)=bx+βx⋯(1)a f(x)+\alpha f\left(\frac1x\right)=bx+\frac{\beta}{x} \quad \cdots (1)af(x)+αf(x1​)=bx+xβ​⋯(1)

Replacing xxx by 1x\dfrac1xx1​: af(1x)+αf(x)=bx+βx⋯(2)a f\left(\frac1x\right)+\alpha f(x)=\frac{b}{x}+\beta x \quad \cdots (2)af(x1​)+αf(x)=xb​+βx⋯(2)

  1. Add equations (1) and (2).

Left-hand side: af(x)+αf(1x)+af(1x)+αf(x)a f(x)+\alpha f\left(\frac1x\right)+a f\left(\frac1x\right)+\alpha f(x)af(x)+αf(x1​)+af(x1​)+αf(x) =(a+α)(f(x)+f(1x)).=(a+\alpha)\left(f(x)+f\left(\frac1x\right)\right).=(a+α)(f(x)+f(x1​)).

Since a+α=1a+\alpha=1a+α=1, this becomes f(x)+f(1x).f(x)+f\left(\frac1x\right).f(x)+f(x1​).

Right-hand side: bx+βx+bx+βxbx+\frac{\beta}{x}+\frac{b}{x}+\beta xbx+xβ​+xb​+βx =(b+β)(x+1x).=(b+\beta)\left(x+\frac1x\right).=(b+β)(x+x1​).

Since b+β=2b+\beta=2b+β=2, this becomes 2(x+1x).2\left(x+\frac1x\right).2(x+x1​).

Hence, f(x)+f(1x)=2(x+1x).f(x)+f\left(\frac1x\right)=2\left(x+\frac1x\right).f(x)+f(x1​)=2(x+x1​).

  1. Therefore,
=\frac{2\left(x+\frac1x\right)}{x+\frac1x}=2.$$ So the required integer is $$\boxed{2}.$$
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