Question
The equation of the tangent at vertex to the parabola 4y2 + 6x = 8y + 7 is
- x = 11/6
- y = 2
- x = –11/6
- y = – 2
Hint:
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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