What is Second derivative: Definition and 178 Discussions

In calculus, the second derivative, or the second order derivative, of a function f is the derivative of the derivative of f. Roughly speaking, the second derivative measures how the rate of change of a quantity is itself changing; for example, the second derivative of the position of an object with respect to time is the instantaneous acceleration of the object, or the rate at which the velocity of the object is changing with respect to time. In Leibniz notation:





a

=



d

v



d
t



=




d

2



x



d

t

2





,


{\displaystyle \mathbf {a} ={\frac {d\mathbf {v} }{dt}}={\frac {d^{2}{\boldsymbol {x}}}{dt^{2}}},}
where a is acceleration, v is velocity, t is time, x is position, and d is the instantaneous "delta" or change. The last expression








d

2



x



d

t

2








{\displaystyle {\tfrac {d^{2}{\boldsymbol {x}}}{dt^{2}}}}
is the second derivative of position (x) with respect to time.
On the graph of a function, the second derivative corresponds to the curvature or concavity of the graph. The graph of a function with a positive second derivative is upwardly concave, while the graph of a function with a negative second derivative curves in the opposite way.

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  1. P

    Second derivative of an integral

    Good day, I don't understand the following: \frac{d^{2}}{dt^{2}}\int_{0}^{t}(t-\epsilon )\phi (\epsilon)d\epsilon=\phi''(t) All I know is: \frac{d^{2}}{dt^{2}}\int_{0}^{t}(t-\epsilon )\phi (\epsilon)d\epsilon=\frac{d^{2}}{dt^{2}}\int_{0}^{t}t \cdot \phi...
  2. S

    What is the Second Derivative Test for Identifying Local Extrema?

    Homework Statement \begin{pmatrix} -2 & 0 & 0\\ 0 & -2 & 0\\ 0 & 0 & -2 \end{pmatrix} If I evaluate with eigenvalues, I get: det\begin{pmatrix} -2-\lambda & 0 & 0\\ 0 & -2-\lambda & 0\\ 0 & 0 & -2-\lambda \end{pmatrix}=0 (-2-\lambda{)}((-2-\lambda{)}(-2-\lambda{)})=0 and thus...
  3. C

    Second Derivative of e^t + t^e ?

    Homework Statement Find the second derivative of e^t + t^e : Homework Equations (e^u) = u' * (e^u) The Attempt at a Solution e^t + t^e 1* (e^t) + e*[t^(e-1)] ^^^first derivative (e^t) + e*e[t^{(e-1)-1}] ^^^ 2nd derivative Answer?: (e^t) + e^2[t^(e-2)]
  4. T

    Steady-State Stability and the Second Derivative

    Hi. I have a question about steady-state stability and the second derivative test. I have been reading about it in a book on mathematical modeling, and the section concerns differential equations. I believe this forum is more appropriate than "General Math," but let me know if it is not...
  5. A

    Discontinuous function at second derivative

    Homework Statement http://imageshack.us/photo/my-images/717/unleddym.png/ Homework Equations The Attempt at a Solution I was wondering why the second derivative at t=1 does not exist but exists at the first derivative. What I did was draw the graph of the function, then the...
  6. Z

    Y value for second derivative involving e^y

    Homework Statement If xy + 9e^y = 9e, find the value of y'' at the point where x = 0. Homework Equations product rule The Attempt at a Solution Okay so first I found the first derivative using implicit differentiation and I got: y'=\frac{-y}{x+9e^{y}} then, I found the second...
  7. S

    Significance of the second derivative

    Homework Statement Let y = s(t) represent the number of students who have contracted measles at time t (days). Give an interpretation for each condition: e) s' = 0, s" > 0 The Attempt at a Solution This seems counterintuitive to me, to think that the second derivative is also not...
  8. J

    Implicit Diff: Find 2nd Deriv of x^3 + y^3 = 1

    Homework Statement Find the second derivative of x^3+y^3=1 by implicit differentiation. The Attempt at a Solution I found the first derivative to be x^2/y^2. Do I then use the first derivative and take the derivative of that? I tried to do this, but got stuck on what to do.
  9. N

    Taylor series and second derivative test: the degenerate case.

    Hello! I am wondering if someone could let me know if my understanding is right or wrong. The Taylor series gives the function in the form of a sum of an infinite series. From this an approximation of the change in the function can be derived: f_{a} and f_{a,a} are the first and second...
  10. F

    Second derivative test for functions of 2 variables

    urgent! second derivative test for functions of 2 variables Homework Statement f(x,y)=x^4 - y^2 - 2x^2 + 2y - 7 Homework Equations classify points (0,1) and (-1,1) as local maximum, local minimum or inclusive The Attempt at a Solution f(x,0)=4x^3 - 0 - 4x + 0 - 0 = 4x^3-4x...
  11. C

    Second derivative using implicit differentiation

    Homework Statement x^6 + y^6 = -6 I have to prove that y'' = 30x^4/y^11 Homework Equations The Attempt at a Solution Using implicit differentiation: 6x^5 + 6y^5 dy/dx = 0 6y^5 dy/dx = -6x^5 dy/dx = -x^5/y^5 Quotient Rule: [(y^5)(-5x^4) - (-x^5)(5y^4 dy/dx)] /...
  12. W

    Second Derivative in Terms of Y

    Homework Statement Find the second derivative of 4x^2 + 3x - 9y^2. Answer in terms of y. Homework Equations All derivative formulas. The Attempt at a Solution [PLAIN]http://http://i52.tinypic.com/2w2ptex.jpg I can't get much further than this; the thing that gets me is how to put...
  13. B

    Second derivative - wolfram giving one answer, professor giving another

    Hi everybody. I have a question regarding an example problem at about 22min on this lecture http://ocw.mit.edu/courses/mathematics/18-03-differential-equations-spring-2010/video-lectures/lecture-2-eulers-numerical-method-for-y-f-x-y/ The equation in question is y'=x^{2}-y^{2}. In an...
  14. A

    Solving Second Derivative of sin (2x)^1/2

    Second Derivative Homework Statement f(x) = sin (2x)^1/2 find the f"(x). Homework Equations The Attempt at a Solution I don't know homework to do it...
  15. J

    Using the approximation, explain why the second derivative test works.

    [b]1. Homework Statement [/ Using the approximation, explain why the second derivative test works approximation=f(x0+delta x, y0+delta y) delta x and delta y are small... Homework Equations f(x0+delta x,y0+delta y) The Attempt at a Solution ok so i know the first derivative...
  16. QuarkCharmer

    Second Derivative Test (trig problem)

    Homework Statement I am doing the various ins and outs of curve sketching and the mean value theorem and all that jazz with this function: f(x)=sec(x)+tan(x) Homework Equations The Attempt at a Solution I took the first derivative to be: f'(x)=sec(x)tan(x)+sec^{2}(x) I am having...
  17. N

    Can't find the second derivative, help

    Homework Statement Knowing that: \frac{dz}{dx}=\sqrt{\frac{(-T)^2}{(k*(z-a)*(z-2*b+a)/2-T*cos(phi))^2}-1} What is: \frac{d^2z}{dx^2} ? Homework Equations I'm trying to solve using this general equation I found on Wikipedia...
  18. M

    Second derivative of an autonomous ODE

    Alright. So I have dy/dx = -1-y2. I want to take the second derivative to get some information about the concavity of the solution, but I can't wrap my head around what's really going on. What I think I know: I have an ODE that is dependent on the dependent variable, so my solution will only...
  19. G

    Finding Uncertainty of the Second Derivative

    Hey there, I have a problem to do, in which I need to determine the acceleration of an object and the uncertainty of the acceleration. The position vs. time equation is given by: s(t) = 0.205t2 + 0.3001t Therefore, after differentiation, I can state the the velocity vs. time equation...
  20. M

    Points of Inflection, The Second Derivative Test.

    Hi, I am having a little trouble understanding something my lecturer said about using the table of signs to check whether there exists a point of inflection when y'' = 0. I understand that in order for there to be a point of inflection at x0 say, I require to check the value of y'' at either...
  21. K

    First and second derivative assistance please?

    Homework Statement r = 2/(2 - cos (\pi*t)) Homework Equations N/A The Attempt at a Solution Hello everyone, first I would just like to say (which is obvious since I'm asking :tongue: ) That it's been a long long time since I've had to do derivatives, hence my total cluelessness...
  22. S

    What Is the Second Derivative of f(x^3) Given These Function Relationships?

    Homework Statement if d/dx(f(x)) = g(x) and d/dx(g(x)) = f(x^2), then d^2/dx^2 ( f(x^3) ) = ? Homework Equations The Attempt at a Solution from 1 and 2 we get d.dx(g(x)) = d2/dx2(f(x)) = f(x^2) but then what? That doesn't tell me anything about f(x^3) Please help.
  23. R

    Using Maclaurin's theorem to estimate second derivative

    Homework Statement Use Maclaurin's theorem to estimate d^{2}y/dx^{2} at x=0 It's the deflection of a 2m beam, where x is the distance along the beam, y is the deflection in mm. Homework Equations The Attempt at a Solution I didn't know where to start so I tried to solve it a different...
  24. M

    Understanding the Second Derivative: Solving a Challenging Calculus Problem

    Second derivative... Homework Statement Okay, this is a rough one for me. It was a question I got on my test, and (obviouslly) didnt get right. I am studying all my old exams for my final in 2 days and this is the last of the problems that I can't wrap my head around...any help would be...
  25. M

    How can I find the second derivative of f(x) = 12x(x-1)^3?

    I have this problem for homework dealing with second derivatives and graphs. I have no problem finding derivatives usually, but this one is giving me trouble. I cannot figure out how to get the second derivative. I have an idea of what to do, but need some extra guidance. Find f '(x) where...
  26. T

    Second Derivative of Trigonometric Functions

    Homework Statement Find the second derivative (y") of y=xtanx. The attempt at a solution I got the first derivative (y') y=xtanx y'=x(secx)+tanx I started the second derivative and got stuck y"=xsec^2x+tanx
  27. N

    Sturm-Liouville Like Equation with Boundary Conditions on Second Derivative

    Hello, I am facing a diffusion equation.. \frac{du(x,t)}{dt} = D \frac{d^2u}{dx^2} .. with slightly exotic boundary conditions: u(0,t) = 0 \frac{d^2u(a,t)}{dx^2}+ \alpha \frac{du(a,t)}{dx} = 0 I expected the solution to be relatively easy to find, since separation of variables quickly...
  28. E

    First and second derivative of a parametric

    Homework Statement x = t - e^{t} y = t + e^{-t} Find dy/dx and d^{2}y/dx.Homework Equations Derivative equations.The Attempt at a Solution dy/dt = 1 - e^{-t} dx/dt = 1 - e^{t} The dy/dx I came up with is: dy/dx = (1 - e^{-t}) / (1 - e^{t}) Second derivative I came up with is: d^{2}y/dx = -...
  29. B

    Chain rule with second derivative

    Homework Statement I trying to find the second derivative of xe^x Homework Equations chain rule The Attempt at a Solution Two find the first derivative I use the chain rule. f'(y)g(y)+f(y)g'(y) so I get e^x+xe^x is the second derivative e^x+f'(y)g(y)+f(y)g'(y)...
  30. 6

    Need to find the second derivative of:

    f(x)= 1/125(e5x)(5x-2)I think this is the first derivative but I ain't good at math and gives me some headaches I used the product rule.. but still I have doubts =( f '(x)= 1/125(5)(e5x)(5x-2) + (5)(1/125(e5x) Please help me! :cry: I need to understand how to do this
  31. N

    Taking second derivative of a derivative

    Hello-- I'm in the process of implementing a PML for FDTD modeling. I would like to take the derivative of the partial derivative shown below, but I am uncertain with respect to how I might proceed. \[ \frac{\partial }{{\partial x}} \to \frac{1}{{1 + \frac{{i\sigma \left( x \right)}}{\omega...
  32. L

    Second derivative test when Hessian is Positive Semi-Definite

    Can someone tell me what this actually is. So, in the case when the Hessian is positive (or negative) semidefinite, the second derivative test is inconclusive. However, I think I've read that even in the case where the Hessian is positive semidefinite at a stationary point x, we can still...
  33. K

    Determining the type of critical point when the second derivative test fails

    Homework Statement For example with f(x,y) = x2y + xy2 Homework Equations The Attempt at a Solution Well I know there is a critical point at (0,0). So I calculated the second derivatives but they are all 0 here so that doesn't help. I also tried using the Taylor expansion to...
  34. B

    Second Derivative using Implicit Differentiation

    Homework Statement Find y''(x) of the parametric equation 9x^2+y^2=9 using implicit differentiation. Homework Equations I already came up with y'(x) = -9x/y The Attempt at a Solution Here is what I have for y''(x) so far y''(x) = d/dx (-9xy^-1) =-9(d/dx)(xy^-1)...
  35. A

    Second Derivative of Exponential Function

    Homework Statement Find the second derivative of: e^{ax} and e^{-ax} Homework Equations The Attempt at a Solution The book that I am using seems to have been very vague on how to take the derivatives of exponential functions. I am aware that: \frac {d(e^{x})}...
  36. S

    MATLAB Matlab second derivative approximation

    clear all; nx=50; ny=30; hx=pi/nx; x=linspace(0,pi,nx+1); y=linspace(0,pi,ny+1); x_plus_h=x+hx.*ones(1,nx+1); x_minus_h=x-hx.*ones(1,nx+1); for i=1:nx+1 for j=1:ny+1 f_xx(j,i)=(f9(x_plus_h(i),y(j))-2*f9+f9(x_minus_h(i),y(j)))./(hx.^2); end; end; [xx,yy]=meshgrid(x,y)...
  37. T

    Help finding the second derivative

    Homework Statement f(x)= x^(3)e^(x) Find f'(x) in simplest form. Find f"(x) in simplest form. Homework Equations The Attempt at a Solution I found the first derivative to be: (using the product rule) f'(x) = (e^x)[3x^2] + (x^3)[e^x] f'(x) = 3x^(2)e^(x) + x^(3)e^(x) f'(x) = x^[2]e^[x](3 + x)...
  38. I

    Finding the Second Derivative of a Square Root Function

    Homework Statement Find the exact value of f''(2) if f(x)=\sqrt{3x-4} Homework Equations See above The Attempt at a Solution I've tried to use the product rule to differentiate. f= x(3x -4)^{\frac{1}{2}} f'= (3x -4)^{\frac{1}{2}} + \frac{3}{2}^{\frac{-1}{2}} f''=...
  39. A

    First & Second derivative of a function

    Homework Statement The function Sh(t) = 30[cos(16.04*)]t models the horizantal position of a pellet with respect to time. Find the first & second derivatives of Sh(t). Homework Equations The Attempt at a Solution I attached a word document because I lack the ability to put...
  40. I

    Second Derivative of a Curve: Solving for x | Finding d2y/dx2=0

    Homework Statement A curve has equation y=e^2x-x^2+x-3 , find value of x for which d^2y/dx^2=0. Homework Equations The Attempt at a Solution well. i started by finding out the 1st and 2nd derivative: y=e^2x-x^2+x-3 dy/dx= 2e2^x-2x+1 and d2y/dx2=4e^2x-2 = 0 dy/dx =>2e^2x=2x-1...
  41. S

    Find the second derivative of F (x)

    Homework Statement Assuming sufficient differentiability, find second derivative of F(x) = integ[a,x] (t-x)2 f(t) d(t) Homework Equations Probably Fund.Thm of Calculus and some properties The Attempt at a Solution I really have no idea..I tried evaluating but with t=x but I get...
  42. M

    Second derivative of Pressure with respect to moles?

    binary mixture. Na=moles of a Nb=moles of b (using Peng Robinson Equation of state) (second order partial derivative below) d^2P/(dNa^2) holding T, molar volume, Nb constant I can't figure out how to do this? I know that Peng Robinson is a function of concentration of Na and...
  43. L

    Differentiation, Second Derivative, of Functions Problem

    Homework Statement Suppose f(3)=2 , f'(3)=5 , and f''(3)= -2 . Then d²/dx² (f²(x)) at x=3 is equal to ____? A. -20 B. 20 C. 38 D. 42 E. 10 The Attempt at a Solution I am confused about how to find the function to get the derivative from that function. Any Ideas? Thanks.
  44. V

    Second derivative from parametric form

    If x and y are defined in terms of a third vatiable say t , then to find d2y/dx2 , we cannot find d2y/dt2 and d2x/dt2 and divide them to get d2y/dx2 , i am unable to fingure out the reason for this !
  45. V

    Second derivative test for x^3

    Does the second derivative test fail for x3 at x=0: f'(x)=3x2 f''(x)=6x , for x=0, f'(0)=0 & f''(0)=+ve , so it should be a point of local maxima , but it is not!
  46. K

    Second Derivative of an Implicit function

    How would you find the second derivative of an implicit function? y^2-x^2=16 Heres my attempt: 2y(dy/dx)-2x=0 2y(dy/dx)=2x 2y(dy/dx)/2y=2x/2y dy/dx= x/y This is only the first derivative. I think I'm suppose to plug in dy/dx back into the original equation. Am I on the right track?
  47. B

    Second derivative in Lagrangian

    The Attempt at a Solution I have calculated a Lagrangian for a particular system (I can post the problem upon request). The system has two degrees of freedom, but I have applied a constraint to remove one of the degrees of freedom. In doing so, I have introduced a second time-derivative of the...
  48. I

    Why is the second derivative notation written as d^2y/dx^2?

    I often see the second derivative written down like this: \frac{d^2y}{dx^2} Although it seems more logical to me to write \frac{d^2y}{d^2x^2} Or \frac{d^2y}{(dx)^2} Since it represents \frac{d}{dx} \frac{dy}{dx} Is there any logic behind this or is it just a shortcut notation to omit...
  49. W

    Working out the first and second derivative

    Let f(x)=x^2/(1-x^2 ) a) Find f'(x) b) Find f"(x) For the answer to a) they give f'(x)=2x/〖(1-x^2)〗^2 and for b) f"(x)=2 (1+〖3x〗^2)/〖(1-x^2)〗^3 Now after many rounds of trying i have not been able to get an answer remotely close to what they have given. i don;t know if it is due to me...
  50. M

    Second derivative of sqrt(x) * e^(-x)

    Homework Statement find f''(x) if f(x) = sqrt(x) * e^(-x) and then find the roots of f''(x) // I am trying to do the 2nd derivative test (need f''x) and then find inflection points// Homework Equations my methodology| d/dx sqrt(x) = 1/(2*sqrt(x)) and d/dx e^(-x) = -e^(-x)...
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