Maths Help

SoSolid · 7 May 2006 at 17:04

How does one go about finding points of inflexion on a graph? I have totaly forgot how to do this?

Rich_L · 7 May 2006 at 17:09

Ergh, vague memories say differentiate the equation and solve dy/dx = 0 that's your points of inflection.

Amleto · 7 May 2006 at 17:10

Rich_L said:
Ergh, vague memories say differentiate the equation and solve dy/dx = 0 that's your points of inflection.

And the second derivative must be zero as well. Otherwise you don't know whether it is a max, min, or inflection.

you could alternatively check the sign of the first derivative just to either side of the turning point. If they both have the same sign, then it must be a point of inflection.

Inquisitor · 7 May 2006 at 17:13

Amleto said:
And the second derivative must be zero as well. Otherwise you don't know whether it is a max, min, or inflection

Even if the second derivative is zero, it still might be a maximum or minimum in certain cases.

Amleto · 7 May 2006 at 17:15

Inquisitor said:
Even if the second derivative is zero, it still might be a maximum or minimum in certain cases.

yes, this is true.

spirit · 7 May 2006 at 17:17

for inflection, if the question is find one, and then you can safely bet that when dy/dx = 0 and d2y/dx2 = 0 its inflection, but really u **** plug numbers around it into dy/dx so u get + 0 - or - 0 +

Amleto · 7 May 2006 at 17:22

spirit said:
for inflection, if the question is find one, and then you can safely bet that when dy/dx = 0 and d2y/dx2 = 0 its inflection, but really u **** plug numbers around it into dy/dx so u get + 0 - or - 0 +

erm, for inflection, dy/dx should have the same sign on either side. d2y/dx2 would have a different sign on either side...

spirit · 7 May 2006 at 17:55

thats right, been a long time since ive done any maths at all, my gap year has so screwed my knowledge lol im buggered when i get to uni and 'ave to do abstract maths lol!