Flashcards · 22 cards

Calculus (JAMB bridge)

Say the answer to yourself, then check. Cards you know come back less and less often; cards you don't come back tomorrow.

  1. Rule

    What is the gradient of a curve at a point?

    Answer

    The gradient of the tangent at that point. dydx\dfrac{dy}{dx} gives it at every point.

    xrunrise
    Gradient of a curveThe gradient of the tangent at the point: rise ÷ run
  2. Rule

    Differentiate y=axny = ax^n.

    Answer

    dydx=naxn−1\dfrac{dy}{dx} = nax^{n - 1}: bring the power down, then reduce the power by 1.

    d/dx (a xⁿ) = na xn − 1
    4x³ → 3 × 4x2 = 12x²
    bring the power down, then take 1 off the power; a constant gives 0
    The power ruleBring the power down, then reduce the power by 1
  3. Know it

    How do you differentiate 2x3+x2x\dfrac{2x^3 + x^2}{x}?

    Answer

    Simplify first to 2x2+x2x^2 + x, then differentiate: 4x+14x + 1. Don't differentiate the top and bottom separately.

  4. Rule

    The derivatives of sin⁡x\sin x and cos⁡x\cos x?

    Answer

    ddxsin⁡x=cos⁡x\dfrac{d}{dx}\sin x = \cos x and ddxcos⁡x=−sin⁡x\dfrac{d}{dx}\cos x = -\sin x.

    sin xcos x−sin x−cos xd/dx
    The cycleEach differentiation moves one step round: sin → cos → −sin → −cos → sin
  5. Rule

    The chain rule? Differentiate sin⁡7x\sin 7x.

    Answer

    dydx=dydu×dudx\dfrac{dy}{dx} = \dfrac{dy}{du} \times \dfrac{du}{dx}: outside first, then times the derivative of the inside. So ddxsin⁡7x=7cos⁡7x\dfrac{d}{dx}\sin 7x = 7\cos 7x.

    y = (3x + 1)5
    dy/dx = 5(3x + 1)4 × 3
    differentiate the outside, leaving the inside alone, then × the inside’s derivative
    The chain ruleOutside first, then times the derivative of the inside
  6. Rule

    The product rule?

    Answer

    For y=uvy = uv: dydx=u′v+uv′\dfrac{dy}{dx} = u'v + uv'.

    uvuvδuδvv δuu δv
    The product ruleThe rectangle's area uv grows by v·δu + u·δv
  7. Rule

    The quotient rule?

    Answer

    For y=uvy = \dfrac uv: dydx=vu′−uv′v2\dfrac{dy}{dx} = \dfrac{vu' - uv'}{v^2}.

    d/dx (u ⁄ v) = (v·u′ − u·v′) ⁄ v²
    bottom × derivative of top, minus top × derivative of bottom, all over bottom squared
    The quotient ruleBottom × top′ − top × bottom′, over bottom squared
  8. Rule

    How do you find a maximum or a minimum?

    Answer

    Solve dydx=0\dfrac{dy}{dx} = 0. Then check: d2ydx2<0\dfrac{d^2y}{dx^2} < 0 is a maximum and >0> 0 a minimum, or look at the gradient's sign either side (+ 0 − is a maximum).

    xmaxmin+−−+
    Maximum and minimumFlat tangents; the gradient's sign changes + 0 − at a maximum and − 0 + at a minimum
  9. Know it

    Asked for the maximum value: what do you give?

    Answer

    The yy-value: put the xx you found back into the original function.

  10. Rule

    A circle's radius grows at drdt\dfrac{dr}{dt}. How fast does its area grow?

    Answer

    Chain rule: dAdt=dAdr×drdt=2πr×drdt\dfrac{dA}{dt} = \dfrac{dA}{dr} \times \dfrac{dr}{dt} = 2\pi r \times \dfrac{dr}{dt}.

    dA/dt = dA/dr × dr/dt
    from the formula × the rate you are given
    Connected ratesThe derivative from the formula, times the rate you are given
  11. Rule

    From distance ss to velocity and acceleration?

    Answer

    Differentiate: v=dsdtv = \dfrac{ds}{dt} and a=dvdta = \dfrac{dv}{dt}.

    distance sd/dt →velocity vd/dt →acceleration a
    differentiate to go right; integrate to come back
    MotionDifferentiate distance to get velocity, and velocity to get acceleration
  12. Rule

    Integrate axnax^n.

    Answer

    axn+1n+1+c\dfrac{ax^{n + 1}}{n + 1} + c, for n≠−1n \ne -1: add 1 to the power, divide by the new power, add cc.

    ∫ a xⁿ dx = a xn + 1 ⁄ (n + 1) + c
    add 1 to the power, then divide by the new power; never forget + c (n ≠ −1)
    Integrating a powerAdd 1 to the power, divide by the new power, add c
  13. Rule

    Why the + c+\,c, and how do you find it?

    Answer

    Every curve y=F(x)+cy = F(x) + c has the same gradient. A given point, put into yy, picks out cc.

    xthe given point+ c
    The + c familyEvery curve y = F(x) + c has the same gradient; the given point picks out one
  14. Know it

    What is ∫cos⁡5x dx\int \cos 5x\,dx?

    Answer

    15sin⁡5x+c\dfrac15\sin 5x + c: divide by 5. Check by differentiating your answer.

  15. Rule

    The area under y=f(x)y = f(x) from x=ax = a to x=bx = b?

    Answer

    ∫abf(x) dx=F(b)−F(a)\int_a^b f(x)\,dx = F(b) - F(a).

    xabarea
    Area under a curveThe area from x = a to x = b is the integral of y from a to b
  16. Know it

    Part of the area is below the xx-axis. What do you do?

    Answer

    Integrate each part separately and add their sizes: below the axis the integral comes out negative.

  17. Rule

    The area between two graphs?

    Answer

    Integrate (top − bottom) between the points where they cross.

    xtopbottom
    Area between two graphsIntegrate (top − bottom) between the crossing points
  18. Rule

    The volume when y=f(x)y = f(x) is turned about the xx-axis?

    Answer

    V=π∫aby2 dxV = \pi\int_a^b y^2\,dx: each slice is a disc of radius yy.

    xy
    Volume of revolutionEach slice is a disc of radius y and area πy²
  19. Which method?

    JAMB 1994 · UME · Q40

    Find the point (x,y)(x, y) where the curve y=2x2−2x+3y = 2x^2 - 2x + 3 has gradient 2.

    How do you find the point?

    Answer

    The gradient is dydx=4x−2\dfrac{dy}{dx} = 4x - 2. Set it equal to 2 to find xx, then put xx into the curve for yy.

  20. Which method?

    JAMB 1992 · UME · Q39

    Obtain the maximum value of the function f(x)=x3−12x+11f(x) = x^3 - 12x + 11.

    Which turning point is the maximum?

    Answer

    f′(x)=3x2−12=0f'(x) = 3x^2 - 12 = 0 gives x=±2x = \pm 2. f′′(x)=6xf''(x) = 6x is negative at x=−2x = -2, so the maximum is there. Then work out f(−2)f(-2).

  21. Which method?

    JAMB 2002 · UME · Q47

    A circle with a radius of 5 cm has its radius increasing at the rate of 0.2 cm s−10.2\text{ cm s}^{-1}. What will be the corresponding rate of increase in the area?

    Which rule connects the two rates?

    Answer

    The chain rule: dAdt=dAdr×drdt\dfrac{dA}{dt} = \dfrac{dA}{dr} \times \dfrac{dr}{dt}, with A=πr2A = \pi r^2.

  22. Which method?

    JAMB 1995 · UME · Q40

    Two variables xx and yy are such that dydx=4x−3\frac{dy}{dx} = 4x - 3 and y=5y = 5 when x=2x = 2. Find yy in terms of xx.

    How do you find cc?

    Answer

    Integrate to get y=2x2−3x+cy = 2x^2 - 3x + c, then put in x=2x = 2 and y=5y = 5.