The curve is known as the Folium of Decsartes. In 1638 the famous philosopher, diplomat, soldier and mathematician René Descartes challenged the lawyer and rival mathematician Pierre de Fermat to find the tangent to this curve at an arbitrary point. (4) x³+y³ - 3xy = 0 3 René Descartes (1596-1650) Pierre de Fermat (1601-1665) Fermat easily found the tangent, which is quite impressive since his method pre-dates Calculus by about 40 years! Now, about 400 years later we can find the tangent easily using implicit differentiation: dy dx = (y-x^2)/(y^2-x) Evaluated at the point [a, b] = [2/3,4/3] the gradient is dy da (2/3,4/3) 0 The formula for the equation of the tangent at [a, b] with gradient m is: y-b=m(x-a). m = At the point [a, b] = [2/3,4/3], this can be rewritten as y = The Folium of Descartes (red) and the tangent at [2/3,4/3] (blue) are displayed below. 31
The curve
x^3+y^3−3xy=0
is known as the Folium of Decsartes. In 1638 the famous philosopher, diplomat, soldier and mathematician René Descartes challenged the lawyer and rival mathematician Pierre de Fermat to find the tangent to this curve at an arbitrary point.
Fermat easily found the tangent, which is quite impressive since his method pre-dates Calculus by about 40 years! Now, about 400 years later we can find the tangent easily using implicit
dydx= .
Evaluated at the point [a,b]=[2/3,4/3]=[2/3,4/3] the gradient is
m=dydx(2/3,4/3)(2/3,4/3)= .
The formula for the equation of the tangent at [a,b] with gradient m is:
y−b=m(x−a)
At the point [a,b]=[2/3,4/3]=[2/3,4/3], this can be rewritten as
y== .
The Folium of Descartes (red) and the tangent at [2/3,4/3][2/3,4/3] (blue) are displayed below
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