Question:medium

If the function \(f(x) = ax^3-bx^2-8x-4\) satisfies Roll's theorem in \([1,3]\), if \(f^'(2) = 0\) then \(a-b\) is equal to...

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Use f(1) = f(3) and f'(2) = 0 together.
Updated On: Oct 1, 2026
  • \(2\)
  • \(-2\)
  • \(0\)
  • \(1\)
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The Correct Option is A

Solution and Explanation

Step 1: Alternative route:
Eliminate $4b$ between $13a-4b=8$ and $12a-4b=8$ (the second is $f'(2)=0$ rewritten).

Step 2: Subtract:
$(13a-4b)-(12a-4b)=8-8$ gives $a=0$.

Step 3: Then:
$-4b=8$, so $b=-2$.

Step 4: Answer:
$a-b=2$. Option (A).

Final Answer:
Subtracting the two linear equations gives a = 0. \[ \boxed{A} \]
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