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Easy

Question

The equation of the tangent at vertex to the parabola 4y2 + 6x = 8y + 7 is

  1. x = 11/6    
  2. y = 2    
  3. x = –11/6    
  4. y = – 2    

hintHint:

convert the equation to the whole square form and find the vertex of  the parabola.

The correct answer is: x = 11/6


    x=11/6 
    Vertex of parabola : 4y2+6x=8x+7
    Converting to the whole square form, we get
    (y-1)2=-3/2(x-11/6)
    Vertex : (11/6, 1)
    Slope of the tangent at the vertex : dy/dx = 3/(4y-4)
    m = 3/(4-4) = tan 90.
    Hence, the equation of tangent: x=11/6 since the line is parallel to the y axis

    if the slope of a line is infinite, then it is parallel to the y axis and the equation becomes x=a, where x is the x intercept.
    Slope of the tangent : dy/dx 

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