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. limx→−1(x3+4x−2)
Step 1: Substitute x=−1 into the expression.
limx→−1(x3+4x−2)=(−1)3+4(−1)−2
Step 2: Simplify the expression.
=−1−4−2=−7
The limit is −7.
ii. limx→2x−2x2−4
Step 1: Factor the numerator.
limx→2x−2(x−2)(x+2)
Step 2: Cancel out the common term (x−2).
limx→2(x+2)
Step 3: Substitute x=2 into the simplified expression.
=2+2=4
The limit is 4.
iii. limx→0x2−xx2+1
Step 1: Substitute x=0 into the expression.
(0)2−0(0)2+1=01
Step 2: Since the denominator approaches 0 and the numerator approaches 1, the limit does not exist.
The limit is Does not exist.
Question Two:
2a) Itemize four (4) techniques for evaluating differentiation together with their formula
• Power Rule: If y=xn, then dxdy=nxn−1.
• Product Rule: If y=u(x)v(x), then dxdy=u′(x)v(x)+u(x)v′(x).
• Quotient Rule: If y=v(x)u(x), then dxdy=[v(x)]2u′(x)v(x)−u(x)v′(x).
• Chain Rule: If y=f(g(x)), then dxdy=f′(g(x))⋅g′(x).
2b) if y=x2, differentiate using the first principle
The first principle definition of the derivative is dxdy=limh→0hf(x+h)−f(x).
Step 1: Substitute f(x)=x2 into the formula.
dxdy=limh→0h(x+h)2−x2
Step 2: Expand (x+h)2.
=limh→0hx2+2xh+h2−x2
Step 3: Simplify the numerator.
=limh→0h2xh+h2
Step 4: Factor out h from the numerator.
=limh→0hh(2x+h)
Step 5: Cancel h and substitute h=0.
=limh→0(2x+h)=2x+0=2x
The derivative is 2x.
2c) Find the derivatives of the following with respect to x using appropriate techniques of differentiation
i. y=(x2+2)5
Step 1: Apply the chain rule. Let u=x2+2, so y=u5. Then dudy=5u4 and dxdu=2x.
Step 2: Multiply dudy by dxdu.
dxdy=5(x2+2)4⋅(2x)
Step 3: Simplify the expression.
dxdy=10x(x2+2)4
The derivative is 10x(x2+2)4.
ii. y=cosxsinx
Step 1: Recognize that y=tanx.
Step 2: Differentiate y=tanx.
dxdy=sec2x
Alternatively, using the quotient rule:
Step 1: Let u=sinx and v=cosx. Then u′=cosx and v′=−sinx.
Step 2: Apply the quotient rule dxdy=v2u′v−uv′.
dxdy=(cosx)2(cosx)(cosx)−(sinx)(−sinx)
Step 3: Simplify the numerator.
=cos2xcos2x+sin2x
Step 4: Use the identity sin2x+cos2x=1.
=cos2x1
Step 5: Rewrite in terms of secx.
=sec2x
The derivative is sec2x.
Question Three:
3a) Differentiate y=exlogex using product rule.
Step 1: Identify u=ex and v=logex.
Step 2: Find the derivatives u′ and v′.
u′=dxd(ex)=ex
v′=dxd(logex)=x1
Step 3: Apply the product rule: dxdy=u′v+uv′.
dxdy=(ex)(logex)+(ex)(x1)
Step 4: Factor out ex.
dxdy=ex(logex+x1)
The derivative is \boxed{e^x \left(\log_e x + \frac{1{x}\right)}}.
3b) Find dxdy, if x2+y2+xy3=3 at the given point (1,1).
Step 1: Differentiate both sides of the equation with respect to x. Remember to use the chain rule for terms involving y and the product rule for xy3.
dxd(x2)+dxd(y2)+dxd(xy3)=dxd(3)
2x+2ydxdy+(1⋅y3+x⋅3y2dxdy)=0
Step 2: Group terms with dxdy.
2x+y3+(2y+3xy2)dxdy=0
Step 3: Isolate dxdy.
(2y+3xy2)dxdy=−2x−y3
dxdy=2y+3xy2−2x−y3
Step 4: Substitute the point (x,y)=(1,1) into the expression for dxdy.
dxdy=2(1)+3(1)(1)2−2(1)−(1)3
=2+3−2−1=5−3
At the point (1,1), dxdy is \boxed{-\frac{3{5}}}.
3c) if y=1+tt2, x=1+tt, then find dxdy.
Step 1: Find dtdy using the quotient rule. Let u=t2, v=1+t. Then u′=2t, v′=1.
dtdy=v2u′v−uv′=(1+t)22t(1+t)−t2(1)
=(1+t)22t+2t2−t2=(1+t)2t2+2t
Step 2: Find dtdx using the quotient rule. Let u=t, v=1+t. Then u′=1, v′=1.
dtdx=v2u′v−uv′=(1+t)21(1+t)−t(1)
=(1+t)21+t−t=(1+t)21
Step 3: Use the chain rule for parametric equations: dxdy=dx/dtdy/dt.
dxdy=(1+t)21(1+t)2t2+2t
Step 4: Simplify the expression.
dxdy=(t2+2t)⋅1(1+t)2=t2+2t
The derivative is t2+2t.
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