You’re correct. It is the point where the double derivative is equal to 0. There are many geometrical intuitions. For cubic equations, the inflection point serves as the point where there is rotational symmetry. This means that you can rotate a cubic function 180 degrees around the inflection point and still have the same plot. I actually cut this part out as it felt like a digression and I didnt want to prolong the video any more than necessary. Maybe I should have kept it in 😭😂
I think this is a great explanation! My only thing would be that some of the equation transformations are hard to follow, since they're so rapid fire. Keep up the good work!
Thank you for the feedback. Rewatching the video now, I understand that the transformation might have been a bit too rapid. Will take that into consideration for the next videos! 😄
It is explained at around 06:09 in the video, but maybe not well enough so I’ll try again haha. The «x» value for the inflection point is found by setting f’’(x) = 0. For a general cubic function f(x) = ax^3 + bx^2 + cx + d, the double derivative f’’(x) = 6ax + 2b If we want the inflection point, we have to set f’’(x) = 0, which will give us 0 = 6ax + 2b which in turn will give us x = -b/(3a). This means that we can find the inflection point for any cubic function at -b/(3a). Now, if we want the inflection point at x = 0, we will get that 0 = -b/(3a) which equates to b = 0. If we go back to our initial equation f(x) and set b = 0, we will get f(x) = ax^3 + 0*x^2 + cx + d. This eliminates the x^2 term as we multiply by zero, and leave us with f(x) = ax^3 + cx + d which essentially is a depressed cubic function. I hope this cleared any doubt. Please let me know if there is anything else! 😄
At 2:03 I have a doubt you took the m×x cube divided it into 3 parts and then place that on the other cube but you only covered 3 sides and not all 6...so vol will be 1/2 of t^3 no ?
Great suggestion! I’ll give it a try if I can find a compelling way to visualize both the problem and the solution. However, the extra dimension might make it challenging :/
Nope there are 3 results: 2, 3.17, and 17.1 approx; calculated from the last formula, the ± on the √ gives 4 variations, the 1st and 4th are the same, the 2nd & 3rd give the other 2 results, and there are 2 cubic roots, that's 3 results each
Very much a valid concern! From 5:04, you will see that we first solve for "t". Then, since u=m/t, we substitute in that solution for "t". However, since the baseline is that "u" is a function of t, we must pick the same t. Hence, two variations. In other words, x = t - u/3. Since u = m/t, we substitute u in the formula for x. Therefore, we get that x = t - m/(3t). This practically means that in the written out formula for x, which you see at 5:14, the cube root terms has to be the same. This is why 5.46 and -1.46 (suppose the other two variations) are not valid solutions in 7:47. Don't fully get how you got 3.17 and 17.1 (?) When that's said, I fully understand the confusion which can occur when simply looking at the formula. To avoid the confusion, you could write x = t - m/(3t) and have the definition of "t" written right besides. Let me know if anything! 😃
@@far1din Yes, I'm confused; Hubris, the pretext humans make "when they have figured out the Universe" ha! 😊 People in Marh/Science like to discard results they don't want, as simple as that, even when clearly the results should be more, but people don't search for the truth, they search for some, convenient truth
That intro was so well done! Still watching but just wanted to say that before I forget
❤❤
Sorry if this sound silly but what actually is inflection point ? is it f" or any other geometric intuition ?
You’re correct. It is the point where the double derivative is equal to 0.
There are many geometrical intuitions. For cubic equations, the inflection point serves as the point where there is rotational symmetry. This means that you can rotate a cubic function 180 degrees around the inflection point and still have the same plot. I actually cut this part out as it felt like a digression and I didnt want to prolong the video any more than necessary. Maybe I should have kept it in 😭😂
If you already made it the better idea would have been to keep it...but btw ty❤@@far1din
I think this is a great explanation! My only thing would be that some of the equation transformations are hard to follow, since they're so rapid fire. Keep up the good work!
Thank you for the feedback. Rewatching the video now, I understand that the transformation might have been a bit too rapid. Will take that into consideration for the next videos! 😄
Great video!! Just one question, why does the inflection point of a depressed cubic fall on x=0?
It is explained at around 06:09 in the video, but maybe not well enough so I’ll try again haha.
The «x» value for the inflection point is found by setting f’’(x) = 0. For a general cubic function f(x) = ax^3 + bx^2 + cx + d, the double derivative f’’(x) = 6ax + 2b
If we want the inflection point, we have to set f’’(x) = 0, which will give us 0 = 6ax + 2b which in turn will give us x = -b/(3a). This means that we can find the inflection point for any cubic function at -b/(3a).
Now, if we want the inflection point at x = 0, we will get that 0 = -b/(3a) which equates to b = 0. If we go back to our initial equation f(x) and set b = 0, we will get f(x) = ax^3 + 0*x^2 + cx + d. This eliminates the x^2 term as we multiply by zero, and leave us with f(x) = ax^3 + cx + d which essentially is a depressed cubic function.
I hope this cleared any doubt. Please let me know if there is anything else! 😄
@@far1din Ah I see, thank you, that explains it pretty well. Cheers on your future videos!
At 2:03 I have a doubt you took the m×x cube divided it into 3 parts and then place that on the other cube but you only covered 3 sides and not all 6...so vol will be 1/2 of t^3 no ?
Sorry now I got it 😅 it was still somewhat subtle confusion..
Haha nice! You’ll see that it is a «cube» with sidelengths = t once it starts spinning. 😄
Nice ! Would you do the same for degree 4?
Great suggestion! I’ll give it a try if I can find a compelling way to visualize both the problem and the solution. However, the extra dimension might make it challenging :/
@@far1din you can add colour to visualise it for example, or draw the projection in R³, there is many way to represent a tesseract
Thanks! This is a complete way to visualize cubics
Nope there are 3 results: 2, 3.17, and 17.1 approx; calculated from the last formula, the ± on the √ gives 4 variations, the 1st and 4th are the same, the 2nd & 3rd give the other 2 results, and there are 2 cubic roots, that's 3 results each
Very much a valid concern! From 5:04, you will see that we first solve for "t". Then, since u=m/t, we substitute in that solution for "t". However, since the baseline is that "u" is a function of t, we must pick the same t. Hence, two variations.
In other words, x = t - u/3. Since u = m/t, we substitute u in the formula for x. Therefore, we get that x = t - m/(3t). This practically means that in the written out formula for x, which you see at 5:14, the cube root terms has to be the same. This is why 5.46 and -1.46 (suppose the other two variations) are not valid solutions in 7:47. Don't fully get how you got 3.17 and 17.1 (?)
When that's said, I fully understand the confusion which can occur when simply looking at the formula. To avoid the confusion, you could write x = t - m/(3t) and have the definition of "t" written right besides. Let me know if anything! 😃
@@far1din Yes, I'm confused; Hubris, the pretext humans make "when they have figured out the Universe" ha! 😊
People in Marh/Science like to discard results they don't want, as simple as that, even when clearly the results should be more, but people don't search for the truth, they search for some, convenient truth