In curve sketching with differentiation, the general curves section, there are no points of inflection written for the quadratic curve.
But from -1 to 1 it goes from negative to positive. Not clear as to why this would not be a point of inflection.

My work includes reading and re-reading and re-reading the section Finding points of inflection, and also reviewing the examples given.

X

In curve sketching with differentiation, the general curves section, there are no points of inflection written for the quadratic curve.
But from -1 to 1 it goes from negative to positive. Not clear as to why this would not be a point of inflection.

Relevant page
<a href="https://www.intmath.com/applications-differentiation/5-curve-sketching-differentiation.php">5. Curve Sketching using Differentiation</a>
What I've done so far
My work includes reading and re-reading and re-reading the section Finding points of inflection, and also reviewing the examples given.

@Phinah: Please have another look at the definition of a point of inflection.

It's where the concavity of the curve changes sign. That is, where it changes from a "U shaped" curve to an "n shaped" curve (or vice versa).

However, a quadratic curve (a parabola) is "U shaped" everywhere (or "n shaped" if the number in front of the `x^2` term is negative).

U-shaped (e.g. `y=x^2+2x+5`)

n-shaped (e.g. `y=-x^2-3x+7`)

So it won't have a point of inflection.

X

@Phinah: Please have another look at the definition of a point of inflection.
It's where the <b>concavity</b> of the curve changes sign. That is, where it changes from a "U shaped" curve to an "n shaped" curve (or vice versa).
However, a quadratic curve (a parabola) is "U shaped" everywhere (or "n shaped" if the number in front of the `x^2` term is negative).
<b>U-shaped</b> (e.g. `y=x^2+2x+5`)
[graph]310,250;-4.5,3.5;-0.5,10.3,1,2;x^2+2x+5,[/graph]
<b>n-shaped</b> (e.g. `y=-x^2-3x+7`)
[graph]310,250;-4.5,3.5;-0.5,10.3,1,2;-x^2-3x+7,[/graph]
So it won't have a point of inflection.

Reply

You need to be logged in to reply.

Related Applications of Differentiation questions

curve sketching[Solved!] Wrote you earlier today. Confusion might come from Example 4. Three lines before...phinah 02 Nov 2017, 05:09

Proof of equation[Solved!] hi,
i need the proof of the following equation:
y = (4Rx(L-2x)) / L^2
I shall be...Hasham 16 Nov 2015, 02:08