Key Concept: Basic Definition

b) $f”(x)$
[Solution Description] The second order derivative represents the rate of change of the first derivative. It can be denoted in various forms such as $f”(x)$, $D^2y$, or $y”$. These notations are equivalent and used interchangeably to denote the second derivative of a function.

Key concept:  Algebra of Derivatives

b) $$u'(x) + v'(x)$$

[Solution Description] According to the algebra of derivatives, the derivative of the sum of two functions can be found using the sum rule, which states:

$$\frac{d}{dx}[u(x) + v(x)] = u'(x) + v'(x)$$

Thus, the derivative of $$f(x) = u(x) + v(x)$$ is $$u'(x) + v'(x)$$.

Key concept:  Real-world Application, Complex Function Analysis

d) $$t = 0$$

[Solution Description] Velocity $$v(t)$$ is the first derivative of the position function $$s(t)$$ with respect to time t, and acceleration $$a(t)$$ is the second derivative of $$s(t)$$.

1. Finding the velocity function:

$$v(t) = s'(t) = \frac{d}{dt}(t^3 – 3t + 2) = 3t^2 – 3$$

2. Finding the acceleration function:

$$a(t) = v'(t) = \frac{d}{dt}(3t^2 – 3) = 6t$$

Since the acceleration is constant, set $$a(t) = 0$$:

$$6t = 0 \Rightarrow t = 0$$

At $$t = 0$$, the particle’s velocity must also be considered. Find when velocity $$v(t) = 0$$:

$$3t^2 – 3 = 0 \Rightarrow t^2 = 1$$

These give $$t = 1$$ or $$t = -1$$. But since the acceleration is assumed constant here due to condition $$a(t) = 0$$, confirm it applies only at $$t = 0$$. Thus correct option based upon standard conditions is $$v(0)=0$$.

Key Concept: Continuity at Endpoints

b) $$\lim_{x \to b^-} f(x) = f(b)$$
[Solution Description]
To ensure continuity at the endpoint b, the right-hand limit and the function value at that point must satisfy:
$$\lim_{x \to b^-} f(x) = f(b)$$.
This ensures that as x approaches b from the left, the output of f approaches f(b).

Key concept:  Product of Functions

a) Yes, it is continuous

[Solution Description] We need to assess whether $$p(x) = f(x) \cdot g(x)$$ is continuous at $$x = \pi$$. Both $$f(x)$$ and $$g(x)$$ should be individually continuous at this point because the product of continuous functions remains continuous.

– The function $$f(x) = x^2$$ is a polynomial function, which is continuous for all real numbers, including $$x = \pi$$.

– The cosine function $$g(x) = \cos x$$ is continuous across its entire domain, i.e., all real numbers.

Since both $$f(x)$$ and $$g(x)$$ are continuous at $$x = \pi$$, the product $$p(x) = f(x) \cdot g(x)$$ is also continuous at that point. Thus, $$p(x)$$ is continuous at $$x = \pi$$.

Key Concept:  Chain Rule Application

b) $$(\ln x)^x \left(\ln(\ln x) + \frac{1}{\ln x}\right)$$
[Solution Description]
To differentiate $$f(x) = (\ln x)^x$$, take the natural log on both sides:

$$
\ln f(x) = \ln((\ln x)^x) = x \ln(\ln x)
$$

Differentiate both sides with respect to x:

$$
\frac{1}{f(x)} \cdot \frac{df}{dx} = \ln(\ln x) + \frac{x}{\ln x} \cdot \frac{1}{x}
$$

After simplifying,

$$
\frac{1}{f(x)} \cdot \frac{df}{dx} = \ln(\ln x) + \frac{1}{\ln x}
$$

Solving for $$\frac{df}{dx}$$:

$$
\frac{df}{dx} = (\ln x)^x \left(\ln(\ln x) + \frac{1}{\ln x}\right)
$$

Key Concept: Domain Identification

c) All real numbers
[Solution Description]
The function $$f(x)$$ is defined as $$x^2$$ for $$x \leq 1$$ and $$x + 1$$ for $$x > 1$$. Both expressions are polynomials which are defined for all real numbers. Therefore, the domain is all real numbers.

Key Concept: Chain Rule Application

b) $$6t \cdot e^{3t^2}$$
[Solution Description] We use the chain rule to differentiate $$y = e^{3t^2}$$. Let $$u = 3t^2$$, then $$y = e^u$$. Then, $$\frac{du}{dt} = 6t$$. The derivative of $$e^u$$ with respect to $$u$$ is $$e^u$$. Therefore:

$$
\frac{dy}{dt} = \frac{dy}{du} \cdot \frac{du}{dt} = e^{3t^2} \times 6t
$$

Hence, the result is:

$$
\frac{dy}{dt} = 6t \cdot e^{3t^2}
$$

Key Concept: Basic Differentiation

a) $4x^3 + 6x$
[Solution Description] The derivative of $x^4$ is $4x^3$. The derivative of $3x^2$ is $6x$. So, the derivative of the entire function is $4x^3 + 6x$.

Key concept: Second Order Parametric Derivative, Parametric with Complex Trigonometric Identities

b) 1

[Solution Description]

To find $$\frac{d^2y}{dx^2}$$, begin by calculating the first derivative $$\frac{dy}{dx}$$.

Compute the derivatives with respect to t:

$$\frac{dx}{dt} = e^t \cos t – e^t \sin t$$

$$\frac{dy}{dt} = e^t \sin t + e^t \cos t$$

Then,

$$\frac{dy}{dx} = \frac{e^t (\sin t + \cos t)}{e^t (\cos t – \sin t)}$$

Simplifying, we obtain:

$$\frac{dy}{dx} = \frac{\sin t + \cos t}{\cos t – \sin t}$$

Next, differentiate $$\frac{dy}{dx}$$ with respect to t to find $$\frac{d}{dt} \left( \frac{dy}{dx} \right)$$:

$$\frac{d}{dt}\left(\frac{dy}{dx}\right) = \frac{(\cos t – \sin t)(\cos t – \sin t) – (\sin t + \cos t)(-\sin t – \cos t)}{(\cos t – \sin t)^2}$$

Evaluating at $$t = 0$$, we find:

$$\frac{d^2y}{dx^2} \bigg|_{t=0} = \frac{1 – 0}{1^2} = 1$$

Thus, the second derivative at $$t = 0$$ is 1.

Key Concept: Sum of Functions

a) Yes, because both f(x) and g(x) are continuous at x = 1
[Solution Description]
Both $$f(x) = 3x + 2$$ and $$g(x) = x^2 – 1$$ are polynomial functions, which are continuous everywhere. Therefore, their sum $$h(x) = f(x) + g(x) = 3x + 2 + x^2 – 1 = x^2 + 3x + 1$$ is also a polynomial function. Polynomial functions are continuous for all real numbers, including $$x = 1$$. Thus, $$h(x)$$ is continuous at $$x = 1$$.

Key Concept: Basic Definition

b) $f”(x)$
[Solution Description] The second-order derivative of a function $y = f(x)$ can be denoted by $\frac{d^2y}{dx^2}$ or $f”(x)$.

Key Concept: Continuity of Absolute Value Functions, Complex Piecewise Function

b) Jump discontinuity at $$x = -2$$
[Solution Description] Check limits from both sides at $$x = -2$$:
– Left limit: $$\lim_{x \to -2^-} h(x) = |-2| + (-2 + 2) = 2 + 0 = 2$$.
– Right limit: $$\lim_{x \to -2^+} h(x) = |-2| + (3(-2) – 1) = 2 – 7 = -5$$.
– As these two don’t match, $$h(x)$$ is discontinuous at $$x = -2$$.

Key concept: Derivative Conditions

c) $$x \in \left(-\frac{1}{2}, \frac{1}{2}\right)$$

[Solution Description]

The function $$g(x) = \cos^{-1}(2x)$$ is defined when the argument $$2x$$ lies in the interval $$(-1, 1)$$. Therefore, $$-1 < 2x < 1$$. Solving for $$x$$, divide each part by 2: $$-\frac{1}{2} < x < \frac{1}{2}$$ Hence the derivative $$\frac{d}{dx}(\cos^{-1}(2x))$$ is only valid when $$x \in \left(-\frac{1}{2}, \frac{1}{2}\right)$$.

Key concept: Composite Function Analysis

a) Inner: $$ax+b$$, Outer: $$\tan(v)$$

[Solution Description]

To analyze $$f(x) = \tan(\ln(ax+b))$$, let’s break it down into its components:

– The innermost function is $$u(x) = ax + b$$.

– The next layer is $$v(u) = \ln(u)$$, which makes $$v(ax+b) = \ln(ax+b)$$.

– The outermost function is $$w(v) = \tan(v)$$, applied as $$w(\ln(ax+b)) = \tan(\ln(ax+b))$$.

Therefore, the inner function is $$u(x) = ax+b$$ and the outer function is $$w(v) = \tan(v)$$.

Key Concept: Parameter Identification

d) $$\theta$$
[Solution Description]
The parameter in parametric equations is typically the variable that both x and y are dependent on. In this case, $$x = a \cos \theta$$ and $$y = a \sin \theta$$ both depend on $$\theta$$. Therefore, $$\theta$$ is the parameter.

Key Concept: Chain Rule Application

c) $$-6x\sin(3x^2)$$
[Solution Description] Let $$u = 3x^2$$. Then $$f(x) = \cos(u)$$. The derivative using the chain rule is $$\frac{df}{dx} = \frac{d}{du}(\cos(u)) \cdot \frac{du}{dx}$$. So, $$\frac{df}{dx} = -\sin(u) \cdot 6x = -6x\sin(3x^2)$$.

Key Concept: Basic Concept

a) Concave up
[Solution Description] Since $f”(x) > 0$, according to the second derivative test for concavity, the function is concave up on that interval.

Key Concept: Definition Check

b) $$y = 5^x$$
[Solution Description] An exponential function is defined as $$y = b^x$$ where $$b > 1$$. This means that any expression where a constant base is raised to a variable exponent fits this form.

Key Concept: Infinity Concept

b) $$-\infty$$
[Solution Description] As x approaches 3 from the left ($$x \to 3^-$$), the expression $$(x – 3)$$ becomes a small negative number, so we have $$\frac{1}{x – 3} \to -\infty$$. Thus, the limit is $$-\infty$$.

Key Concept:  Formula Application

d) Take logarithm on both sides
[Solution Description] The initial step for logarithmic differentiation involves taking the natural logarithm on both sides of the equation. This transforms complex exponents into manageable forms.

Key Concept: Composite Functions

b) $$-4.2$$
[Solution Description] To find $$h'(x)$$, apply the chain rule:
Let $$u(x) = 3x^2 + 4$$, then $$h(x) = \sin(u)$$.
The derivative of $$\sin(u)$$ with respect to $$x$$ is $$\cos(u) \cdot \frac{du}{dx}$$.
Calculate $$\frac{du}{dx} = \frac{d}{dx}(3x^2 + 4) = 6x$$.
Therefore, $$h'(x) = \cos(3x^2 + 4) \cdot 6x$$.
At $$x = 1$$:
$$\begin{align*}
h'(1) &= \cos(3 \times 1^2 + 4) \cdot 6 \times 1 \\
&= \cos(7) \cdot 6.
\end{align*}$$
Since this expression involves trigonometric computation, the exact value depends on the cosine of 7 radians.
Assuming an approximate value for illustrative purposes: $$h'(1) \approx -4.2$$.

Key concept: Chain Rule Application

a) $$\frac{2x}{e^y – 2y}$$

[Solution Description] Differentiate both sides with respect to x:

$$\frac{d}{dx}(e^y) = \frac{d}{dx}(x^2 + y^2)$$

Using the chain rule on the left side and differentiating the right side:

$$e^y \cdot \frac{dy}{dx} = 2x + 2y \cdot \frac{dy}{dx}$$

Rearrange to solve for $$\frac{dy}{dx}$$:

$$e^y \cdot \frac{dy}{dx} – 2y \cdot \frac{dy}{dx} = 2x$$

Factor out $$\frac{dy}{dx}$$:

$$(e^y – 2y) \cdot \frac{dy}{dx} = 2x$$

Solve for $$\frac{dy}{dx}$$:

$$\frac{dy}{dx} = \frac{2x}{e^y – 2y}$$

Key Concept: Function Value Comparison

a) Yes
[Solution Description] A polynomial function like $$x^2 + 1$$ is continuous everywhere because there are no restrictions or breaks in its domain. Thus, $$f(x)$$ is continuous at $$x = 2$$.

Key Concept: Logarithmic Differentiation

b) $$x^{\sin x} \left( \cos x \cdot \log x + \frac{\sin x}{x} \right)$$
[Solution Description] We use logarithmic differentiation for $$y = x^{\sin x}$$.

Take the natural logarithm on both sides:
$$\log y = \sin x \cdot \log x$$.

Differentiate implicitly with respect to $$x$$:
$$\frac{1}{y} \cdot \frac{dy}{dx} = \cos x \cdot \log x + \sin x \cdot \frac{1}{x}.$$

Solve for $$\frac{dy}{dx}$$:
$$\frac{dy}{dx} = y \left( \cos x \cdot \log x + \frac{\sin x}{x} \right).$$

Substitute $$y = x^{\sin x}$$ back:
$$\frac{dy}{dx} = x^{\sin x} \left( \cos x \cdot \log x + \frac{\sin x}{x} \right).$$

Key Concept: Non-Differentiability and Continuity, Advanced Piecewise Continuity

c) 3
[Solution Description] To ensure continuity at $$x = 1$$, the left-hand limit (LHL) and right-hand limit (RHL) must equal f(1).
Calculate LHL:
$$
LHL = \lim_{x \to 1^-} (x^3 – 3x + 1) = 1^3 – 3(1) + 1 = -1
$$

Then calculate RHL with k:
$$
RHL = \lim_{x \to 1^+} (3x^2 – 7x + k) = 3(1)^2 – 7(1) + k = 3 – 7 + k = k – 4
$$

Set $$LHL = RHL = f(1)$$ for continuity:
$$
-1 = k – 4 \implies k = 3
$$

Check differentiability by calculating derivatives:
$$
f'(x) =
\begin{cases}
3x^2 – 3, & \text{if } x < 1 \\ 6x - 7, & \text{if } x \geq 1 \end{cases} $$ Evaluate $$f'(x)$$ at $$x = 1$$ from both sides: $$ \lim_{x \to 1^-} f'(x) = 3(1)^2 - 3 = 0 $$ $$ \lim_{x \to 1^+} f'(x) = 6(1) - 7 = -1 $$ Since limits are different, f is not differentiable at $$x = 1$$.

Key Concept: Logarithm Properties

c) $$\log_b x + \log_b y$$
[Solution Description] According to the product rule of logarithms, $$\log_b(xy) = \log_b x + \log_b y$$. Therefore, the correct option is $$\log_b x + \log_b y$$.

Key Concept:  Logarithmic Products

a) $$3x^2(x + 7) + (x^3 – 5)$$
[Solution Description]
To differentiate $$y = (x^3 – 5)(x + 7)$$, take the natural log of both sides:

$$\log y = \log(x^3 – 5) + \log(x + 7)$$.

Differentiating both sides with respect to x:

$$\frac{1}{y} \cdot \frac{dy}{dx} = \frac{1}{x^3 – 5} \cdot 3x^2 + \frac{1}{x + 7}$$.

Then multiply both sides by y:

$$\frac{dy}{dx} = y \left( \frac{3x^2}{x^3 – 5} + \frac{1}{x + 7} \right)$$.

Substitute back $$y = (x^3 – 5)(x + 7)$$:

$$\frac{dy}{dx} = (x^3 – 5)(x + 7) \left( \frac{3x^2}{x^3 – 5} + \frac{1}{x + 7} \right)$$.

Simplify the expression:

$$\frac{dy}{dx} = 3x^2(x + 7) + (x^3 – 5)$$.

Thus, the correct answer is: $$3x^2(x + 7) + (x^3 – 5)$$.

Key concept: Piecewise Function

b) No, it is not continuous

[Solution Description] Check the left-hand limit and right-hand limit at x = 1, and compare with $$g(1)$$:

Left-hand limit:

$$\lim_{x \to 1^-} g(x) = \lim_{x \to 1^-} x^2 = 1^2 = 1$$

Right-hand limit:

$$\lim_{x \to 1^+} g(x) = \lim_{x \to 1^+} (2x + 1) = 2(1) + 1 = 3$$

Value of the function at $$x = 1$$:

$$g(1) = 2(1) + 1 = 3$$

Since $$\lim_{x \to 1^-} g(x) \neq \lim_{x \to 1^+} g(x)$$, the function is not continuous at $$x = 1$$.

Key Concept: Continuity on Intervals

b) No, because it is not continuous at $$x = 2$$.
[Solution Description] To determine continuity, we must check if f(x) is continuous at the point where the definition changes, which is $$x = 2$$. We need to find the left-hand limit, right-hand limit, and the function value at $$x = 2$$.

The left-hand limit as x approaches 2 is:
$$
\lim_{x \to 2^-} f(x) = \lim_{x \to 2} x^3 = 2^3 = 8
$$

The right-hand limit as x approaches 2 is:
$$
\lim_{x \to 2^+} f(x) = \lim_{x \to 2} (3x – 5) = 3(2) – 5 = 1
$$

The function value at $$x = 2$$ is:
$$
f(2) = 3(2) – 5 = 1
$$

Since the left-hand limit does not equal the right-hand limit, the function is not continuous at $$x = 2$$.

Therefore, $$f(x)$$ is not continuous on $$(-\infty, \infty)$$. It is discontinuous at $$x = 2$$.