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The equation of the tangent to the curve y=(x3)(x1)(x2)y = \frac{(x - 3)}{(x - 1)(x - 2)} at the point, where it cuts x-axis is:

Solution

Correct Option: 3

When a curve "cuts the x-axis," it crosses the x-axis where y=0y = 0.

Set y=0y = 0:

0=(x3)(x1)(x2)0 = \frac{(x - 3)}{(x - 1)(x - 2)}

A fraction equals zero only when its numerator is zero (and denominator is not zero).

x3=0x - 3 = 0

x=3x = 3

The curve cuts the x-axis at the point (3,0)(3, 0).


To find the slope of the tangent at (3,0)(3, 0), find the derivative dydx\frac{dy}{dx}.

Given: y=(x3)(x1)(x2)y = \frac{(x - 3)}{(x - 1)(x - 2)}

Using the Quotient Rule: dydx=uvuvv2\frac{dy}{dx} = \frac{u'v - uv'}{v^2}

Where:

  • u=(x3)u = (x - 3), so u=1u' = 1
  • v=(x1)(x2)=x23x+2v = (x - 1)(x - 2) = x^2 - 3x + 2, so v=2x3v' = 2x - 3

dydx=1(x23x+2)(x3)(2x3)[(x1)(x2)]2\frac{dy}{dx} = \frac{1 \cdot (x^2 - 3x + 2) - (x - 3)(2x - 3)}{[(x - 1)(x - 2)]^2}

Simplifying the numerator:

(x23x+2)(x3)(2x3)(x^2 - 3x + 2) - (x - 3)(2x - 3)

=x23x+2(2x23x6x+9)= x^2 - 3x + 2 - (2x^2 - 3x - 6x + 9)

=x23x+22x2+9x9= x^2 - 3x + 2 - 2x^2 + 9x - 9

=x2+6x7= -x^2 + 6x - 7

At x=3x = 3:

Numerator: (3)2+6(3)7=9+187=2-(3)^2 + 6(3) - 7 = -9 + 18 - 7 = 2

Denominator: [(31)(32)]2=[2×1]2=4[(3-1)(3-2)]^2 = [2 \times 1]^2 = 4

Slope =24=12= \frac{2}{4} = \frac{1}{2}


Using point-slope form with point (3,0)(3, 0) and slope m=12m = \frac{1}{2}:

y0=12(x3)y - 0 = \frac{1}{2}(x - 3)

y=12x32y = \frac{1}{2}x - \frac{3}{2}

2y=x32y = x - 3

2yx+3=02y - x + 3 = 0

Therefore, the equation of the tangent is 2yx+3=02y - x + 3 = 0.

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