If $f(x) = g(x)|(x-1)(x-2)\cdots(x-10)| - 2$ is derivable for all $x \in R$, where $g(x) = ax^9 + bx^6 + cx^3 + d$, $a, b, c, d \in R$, then $f'(-1)$ is equal to:
Step-by-Step Solution
Key Concept: A polynomial of degree n cannot have more than n roots unless it is identically zero.
Step 1: Understand the differentiability condition at critical points.
For $f(x) = g(x)|(x-1)(x-2)\cdots(x-10)| - 2$ to be derivable (differentiable) for all $x \in \mathbb{R}$, it must be differentiable at the points where the absolute value expression changes sign, namely at $x = 1, 2, 3, \ldots, 10$.
Step 2: Determine the necessary condition for differentiability at these points.
At each point $x = k$ where $k \in \{1, 2, \ldots, 10\}$, the expression $|(x-1)(x-2)\cdots(x-10)|$ has a corner (non-differentiable point). For $f(x)$ to be differentiable at $x = k$, the factor $g(k)$ must equal zero. This ensures that the product $g(x) \cdot |(x-1)(x-2)\cdots(x-10)|$ remains differentiable at these points.
Therefore, we require:
$$g(1) = g(2) = g(3) = \cdots = g(10) = 0$$
Step 3: Analyze the polynomial $g(x)$ and its roots.
We are given that $g(x) = ax^9 + bx^6 + cx^3 + d$, which is a polynomial of degree at most 9.
However, from Step 2, we need $g(x)$ to have at least 10 roots: $x = 1, 2, 3, \ldots, 10$.
Step 4: Apply the fundamental theorem of algebra.
A polynomial of degree $n$ can have at most $n$ real roots. Since $g(x)$ has degree at most 9, it can have at most 9 roots. But we require it to have 10 roots, which is impossible unless $g(x)$ is the zero polynomial.
Therefore:
$$g(x) \equiv 0 \text{ for all } x \in \mathbb{R}$$
This means $a = b = c = d = 0$.
Step 5: Simplify $f(x)$ and find $f'(-1)$.
With $g(x) = 0$, we have:
$$f(x) = 0 \cdot |(x-1)(x-2)\cdots(x-10)| - 2 = -2$$
Since $f(x) = -2$ is a constant function:
$$f'(-1) = 0$$
**Final Answer:** The value of $f'(-1)$ is $\boxed{0}$, which corresponds to **Option 2**.
Correct Answer: 2