Distinct real roots of quadratic in (x + 1/x)

CAT 2020 Slot 1 · QA · Medium · Quadratic Equations

The number of distinct real roots of the equation (x+1x)23(x+1x)+2=0\left(x + \frac{1}{x}\right)^2 - 3\left(x + \frac{1}{x}\right) + 2 = 0 equals

(TITA)

Answer

1

Explanation

Let y=x+1xy = x + \frac{1}{x}. The equation becomes: y23y+2=0    (y1)(y2)=0y^2 - 3y + 2 = 0 \implies (y - 1)(y - 2) = 0 So y=1y = 1 or y=2y = 2.

  • Case 1: x+1x=1    x2x+1=0x + \frac{1}{x} = 1 \implies x^2 - x + 1 = 0. Discriminant D=14=3<0D = 1 - 4 = -3 < 0, so no real roots.

  • Case 2: x+1x=2    x22x+1=0    (x1)2=0x + \frac{1}{x} = 2 \implies x^2 - 2x + 1 = 0 \implies (x - 1)^2 = 0. This gives x=1x = 1.

Thus, there is only 1 distinct real root.

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