The curve $y=f(x)$ satisfies $\dfrac{d^2y}{dx^2}=6x-4$ and has a local minimum value $5$ at $x=1$. $f(0)$ is
Step-by-Step Solution
Key Concept: Integrate twice, use $f'(1)=0$ and $f(1)=5$
Given the second derivative of the curve $y=f(x)$ as $\dfrac{d^2y}{dx^2}=6x-4$, and that it has a local minimum value $5$ at $x=1$.
Step 1: Integrate the second derivative to find the first derivative.
$$f''(x) = 6x-4$$
$$f'(x) = \int (6x-4) dx = 3x^2 - 4x + C_1$$
Step 2: Use the condition for a local minimum to determine $C_1$.
Since there is a local minimum at $x=1$, we know that $f'(1)=0$.
$$3(1)^2 - 4(1) + C_1 = 0$$
$$3 - 4 + C_1 = 0$$
$$-1 + C_1 = 0$$
$$C_1 = 1$$
Thus, the first derivative is $f'(x) = 3x^2 - 4x + 1$.
Step 3: Integrate the first derivative to find the function $f(x)$.
$$f(x) = \int (3x^2 - 4x + 1) dx = x^3 - 2x^2 + x + C_2$$
Step 4: Use the local minimum value to determine $C_2$.
The local minimum value is $5$ at $x=1$, which means $f(1)=5$.
$$(1)^3 - 2(1)^2 + (1) + C_2 = 5$$
$$1 - 2 + 1 + C_2 = 5$$
$$0 + C_2 = 5$$
$$C_2 = 5$$
Thus, the function is $f(x) = x^3 - 2x^2 + x + 5$.
Step 5: Calculate $f(0)$.
Substitute $x=0$ into the function $f(x)$:
$$f(0) = (0)^3 - 2(0)^2 + (0) + 5$$
$$f(0) = 0 - 0 + 0 + 5$$
$$f(0) = 5$$
Correct Answer: 3