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Define limit of a function. List the methods for evaluating the limits of a function. Evaluate the limits of the following functions. Itemize four (4) techniques for evaluating differentiation together with their formula.

Mathematics

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Question One:

1a) Define limit of a function
A limit of a function describes the value that a function "approaches" as the input (or independent variable) approaches a certain value. It is a fundamental concept in calculus for defining continuity, derivatives, and integrals.

1b) List the methods for evaluating the limits of a function

  • Direct Substitution
  • Factoring and Cancellation
  • Rationalization
  • L'Hôpital's Rule
  • Squeeze Theorem
  • Using known limits (e.g., trigonometric limits)

1c) Evaluate the limits of the following functions

i. lim⁡x→−1(x3+4x−2)\lim_{x \to -1} (x^3 + 4x - 2)

  1. Substitute x=−1x = -1 into the expression.

    lim⁡x→−1(x3+4x−2)=(−1)3+4(−1)−2\lim_{x \to -1} (x^3 + 4x - 2) = (-1)^3 + 4(-1) - 2
  2. Simplify the expression.

    =−1−4−2=−7= -1 - 4 - 2 = -7

    The limit is −7\boxed{\mathbf{-7}}.

    ii. lim⁡x→2x2−4x−2\lim_{x \to 2} \frac{x^2 - 4}{x - 2}

  3. Factor the numerator.

    lim⁡x→2(x−2)(x+2)x−2\lim_{x \to 2} \frac{(x - 2)(x + 2)}{x - 2}
  4. Cancel out the common term (x−2)(x - 2).

    lim⁡x→2(x+2)\lim_{x \to 2} (x + 2)
  5. Substitute x=2x = 2 into the simplified expression.

    =2+2=4= 2 + 2 = 4

    The limit is 4\boxed{\mathbf{4}}.

    iii. lim⁡x→0x2+1x2−x\lim_{x \to 0} \frac{x^2 + 1}{x^2 - x}

  6. Substitute x=0x = 0 into the expression.

    (0)2+1(0)2−0=10\frac{(0)^2 + 1}{(0)^2 - 0} = \frac{1}{0}
  7. Since the denominator approaches 0 and the numerator approaches 1, the limit does not exist.

    The limit is Does not exist\boxed{\mathbf{Does\ not\ exist}}.

    Question Two:

    2a) Itemize four (4) techniques for evaluating differentiation together with their formula

    • Power Rule: If y=xny = x^n, then dydx=nxn−1\frac{dy}{dx} = nx^{n-1}.
    • Product Rule: If y=u(x)v(x)y = u(x)v(x), then dydx=u′(x)v(x)+u(x)v′(x)\frac{dy}{dx} = u'(x)v(x) + u(x)v'(x).
    • Quotient Rule: If y=u(x)v(x)y = \frac{u(x)}{v(x)}, then dydx=u′(x)v(x)−u(x)v′(x)[v(x)]2\frac{dy}{dx} = \frac{u'(x)v(x) - u(x)v'(x)}{[v(x)]^2}.
    • Chain Rule: If y=f(g(x))y = f(g(x)), then dydx=f′(g(x))⋅g′(x)\frac{dy}{dx} = f'(g(x)) \cdot g'(x).

    2b) if y=x2y = x^2, differentiate using the first principle
    The first principle definition of the derivative is dydx=lim⁡h→0f(x+h)−f(x)h\frac{dy}{dx} = \lim_{h \to 0} \frac{f(x+h) - f(x)}{h}.

  8. Substitute f(x)=x2f(x) = x^2 into the formula.

    dydx=lim⁡h→0(x+h)2−x2h\frac{dy}{dx} = \lim_{h \to 0} \frac{(x+h)^2 - x^2}{h}
  9. Expand (x+h)2(x+h)^2.

    =lim⁡h→0x2+2xh+h2−x2h= \lim_{h \to 0} \frac{x^2 + 2xh + h^2 - x^2}{h}
  10. Simplify the numerator.

    =lim⁡h→02xh+h2h= \lim_{h \to 0} \frac{2xh + h^2}{h}
  11. Factor out hh from the numerator.

    =lim⁡h→0h(2x+h)h= \lim_{h \to 0} \frac{h(2x + h)}{h}
  12. Cancel hh and substitute h=0h=0.

    =lim⁡h→0(2x+h)=2x+0=2x= \lim_{h \to 0} (2x + h) = 2x + 0 = 2x

    The derivative is 2x\boxed{\mathbf{2x}}.

    2c) Find the derivatives of the following with respect to x using appropriate techniques of differentiation

    i. y=(x2+2)5y = (x^2 + 2)^5

  13. Apply the chain rule.

    Let u=x2+2u = x^2 + 2, so y=u5y = u^5. Then dydu=5u4\frac{dy}{du} = 5u^4 and dudx=2x\frac{du}{dx} = 2x.

  14. Multiply dydu\frac{dy}{du} by dudx\frac{du}{dx}.

    dydx=5(x2+2)4⋅(2x)\frac{dy}{dx} = 5(x^2 + 2)^4 \cdot (2x)
  15. Simplify the expression.

    dydx=10x(x2+2)4\frac{dy}{dx} = 10x(x^2 + 2)^4

    The derivative is 10x(x2+2)4\boxed{\mathbf{10x(x^2 + 2)^4}}.

    ii. y=sin⁡xcos⁡xy = \frac{\sin x}{\cos x}

  16. Recognize that y=tan⁡xy = \tan x.

  17. Differentiate y=tan⁡xy = \tan x.

    dydx=sec⁡2x\frac{dy}{dx} = \sec^2 x

    Alternatively, using the quotient rule:

  18. Let u=sin⁡xu = \sin x and v=cos⁡xv = \cos x.

    Then u′=cos⁡xu' = \cos x and v′=−sin⁡xv' = -\sin x.

  19. Apply the quotient rule dydx=u′v−uv′v2\frac{dy}{dx} = \frac{u'v - uv'}{v^2}.

    dydx=(cos⁡x)(cos⁡x)−(sin⁡x)(−sin⁡x)(cos⁡x)2\frac{dy}{dx} = \frac{(\cos x)(\cos x) - (\sin x)(-\sin x)}{(\cos x)^2}
  20. Simplify the numerator.

    =cos⁡2x+sin⁡2xcos⁡2x= \frac{\cos^2 x + \sin^2 x}{\cos^2 x}
  21. Use the identity sin⁡2x+cos⁡2x=1\sin^2 x + \cos^2 x = 1.

    =1cos⁡2x= \frac{1}{\cos^2 x}
  22. Rewrite in terms of sec⁡x\sec x.

    =sec⁡2x= \sec^2 x

    The derivative is sec⁡2x\boxed{\mathbf{\sec^2 x}}.

    Question Three:

    3a) Differentiate y=exlog⁡exy = e^x \log_e x using product rule.

  23. Identify u=exu = e^x and v=log⁡exv = \log_e x.

  24. Find the derivatives u′u' and v′v'.

    u′=ddx(ex)=exu' = \frac{d}{dx}(e^x) = e^x v′=ddx(log⁡ex)=1xv' = \frac{d}{dx}(\log_e x) = \frac{1}{x}
  25. Apply the product rule

    dydx=u′v+uv′\frac{dy}{dx} = u'v + uv'.

    dydx=(ex)(log⁡ex)+(ex)(1x)\frac{dy}{dx} = (e^x)(\log_e x) + (e^x)\left(\frac{1}{x}\right)
  26. Factor out exe^x.

    dydx=ex(log⁡ex+1x)\frac{dy}{dx} = e^x \left(\log_e x + \frac{1}{x}\right)

    The derivative is ex(log⁡ex+1x)\boxed{\mathbf{e^x \left(\log_e x + \frac{1}{x}\right)}}.

    3b) Find dydx\frac{dy}{dx}, if x2+y2+xy3=3x^2 + y^2 + xy^3 = 3 at the given point (1,1)(1, 1).

  27. Differentiate both sides of the equation with respect to xx.

    Remember to use the chain rule for terms involving yy and the product rule for xy3xy^3.

    ddx(x2)+ddx(y2)+ddx(xy3)=ddx(3)\frac{d}{dx}(x^2) + \frac{d}{dx}(y^2) + \frac{d}{dx}(xy^3) = \frac{d}{dx}(3) 2x+2ydydx+(1⋅y3+x⋅3y2dydx)=02x + 2y \frac{dy}{dx} + \left(1 \cdot y^3 + x \cdot 3y^2 \frac{dy}{dx}\right) = 0
  28. Group terms with dydx\frac{dy}{dx}.

    2x+y3+(2y+3xy2)dydx=02x + y^3 + (2y + 3xy^2) \frac{dy}{dx} = 0
  29. Isolate dydx\frac{dy}{dx}.

    (2y+3xy2)dydx=−2x−y3(2y + 3xy^2) \frac{dy}{dx} = -2x - y^3 dydx=−2x−y32y+3xy2\frac{dy}{dx} = \frac{-2x - y^3}{2y + 3xy^2}
  30. Substitute the point (x,y)=(1,1)(x, y) = (1, 1) into the expression for dydx\frac{dy}{dx}.

    dydx=−2(1)−(1)32(1)+3(1)(1)2\frac{dy}{dx} = \frac{-2(1) - (1)^3}{2(1) + 3(1)(1)^2} =−2−12+3=−35= \frac{-2 - 1}{2 + 3} = \frac{-3}{5}

    At the point (1,1)(1, 1), dydx\frac{dy}{dx} is −35\boxed{\mathbf{-\frac{3}{5}}}.

    3c) if y=t21+ty = \frac{t^2}{1+t}, x=t1+tx = \frac{t}{1+t}, then find dydx\frac{dy}{dx}.

  31. Find dydt\frac{dy}{dt} using the quotient rule.

    Let u=t2u = t^2, v=1+tv = 1+t. Then u′=2tu' = 2t, v′=1v' = 1.

    dydt=u′v−uv′v2=2t(1+t)−t2(1)(1+t)2\frac{dy}{dt} = \frac{u'v - uv'}{v^2} = \frac{2t(1+t) - t^2(1)}{(1+t)^2} =2t+2t2−t2(1+t)2=t2+2t(1+t)2= \frac{2t + 2t^2 - t^2}{(1+t)^2} = \frac{t^2 + 2t}{(1+t)^2}
  32. Find dxdt\frac{dx}{dt} using the quotient rule.

    Let u=tu = t, v=1+tv = 1+t. Then u′=1u' = 1, v′=1v' = 1.

    dxdt=u′v−uv′v2=1(1+t)−t(1)(1+t)2\frac{dx}{dt} = \frac{u'v - uv'}{v^2} = \frac{1(1+t) - t(1)}{(1+t)^2} =1+t−t(1+t)2=1(1+t)2= \frac{1+t - t}{(1+t)^2} = \frac{1}{(1+t)^2}
  33. Use the chain rule for parametric equations

    dydx=dy/dtdx/dt\frac{dy}{dx} = \frac{dy/dt}{dx/dt}.

    dydx=t2+2t(1+t)21(1+t)2\frac{dy}{dx} = \frac{\frac{t^2 + 2t}{(1+t)^2}}{\frac{1}{(1+t)^2}}
  34. Simplify the expression.

    dydx=(t2+2t)⋅(1+t)21=t2+2t\frac{dy}{dx} = (t^2 + 2t) \cdot \frac{(1+t)^2}{1} = t^2 + 2t

    The derivative is t2+2t\boxed{\mathbf{t^2 + 2t}}.

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