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For real values of xx, the range of the function f(x)=2x−32x2+4x−6f(x)=\frac{2x-3}{2x^2+4x-6} is

Solution

✅ Correct Option: 2

The denominator can be factored as:

2x2+4x−6=2(x+3)(x−1)2x^2+4x-6 = 2(x+3)(x-1)

The function is undefined at x=1x = 1 and x=−3x = -3.


Let y=f(x)y = f(x) and cross-multiply:

y(2x2+4x−6)=2x−3y(2x^2+4x-6) = 2x-3

2yx2+(4y−2)x+(3−6y)=02yx^2 + (4y-2)x + (3-6y) = 0

For xx to be real, the discriminant of this quadratic must be ≥0\geq 0.


When y=0y = 0, the equation becomes:

−2x+3=0-2x + 3 = 0

x=32x = \dfrac{3}{2}

This is a valid xx-value (not excluded from the domain), so y=0y = 0 is in the range.


When y≠0y \neq 0, applying the discriminant condition Δ≥0\Delta \geq 0:

Δ=(4y−2)2−4(2y)(3−6y)≥0\Delta = (4y-2)^2 - 4(2y)(3-6y) \geq 0

=16y2−16y+4−24y+48y2≥0= 16y^2 - 16y + 4 - 24y + 48y^2 \geq 0

=64y2−40y+4≥0= 64y^2 - 40y + 4 \geq 0

=4(16y2−10y+1)≥0= 4(16y^2 - 10y + 1) \geq 0

16y2−10y+1≥016y^2 - 10y + 1 \geq 0


Roots of 16y2−10y+1=016y^2 - 10y + 1 = 0:

y=10±100−6432y = \dfrac{10 \pm \sqrt{100 - 64}}{32}

=10±632= \dfrac{10 \pm 6}{32}

y=18y = \dfrac{1}{8} or y=12y = \dfrac{1}{2}

Since the coefficient of y2y^2 is positive, the parabola opens upward, so the expression is ≥0\geq 0 outside the roots:

y≤18y \leq \dfrac{1}{8} or y≥12y \geq \dfrac{1}{2}


Checking whether the excluded points x=1x = 1 and x=−3x = -3 affect the range:

Substituting x=1x = 1 into 2yx2+(4y−2)x+(3−6y)=02yx^2 + (4y-2)x + (3-6y) = 0 gives 1=01 = 0.

Substituting x=−3x = -3 gives 9=09 = 0.

Neither excluded point is ever a solution, so no yy-values need to be removed.


Range of f(x)=(−∞, 18]∪[12, ∞)f(x) = \left(-\infty,\, \dfrac{1}{8}\right] \cup \left[\dfrac{1}{2},\, \infty\right)

The correct answer is Option 2.

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