AP EAMCET · Maths · Application of Derivatives

The radius and the height of a right circular solid cone are measured as 7 feet each. If there is an error of 0.002 ft for every feet in measuring them, then the error in the total surface area of the cone (in sq. ft ) is

A \((0.088)(\sqrt{2}+1)\)
B \((0.616)(\sqrt{2}+1)\)
C \((0.616)(\sqrt{2})\)
D \((0.088)(\sqrt{2})\)

Verified Solution

Answer & Solution

Correct Answer

(B) \((0.616)(\sqrt{2}+1)\)

Step-by-step Solution

Detailed explanation

\( r = 7 \text{ ft}, h = 7 \text{ ft} \) \( \Delta r = 0.002r = 0.002 \times 7 = 0.014 \text{ ft} \) \( \Delta h = 0.002h = 0.002 \times 7 = 0.014 \text{ ft} \) \( S = \pi r^2 + \pi r \sqrt{r^2+h^2} \)…

Apply the relevant identity from the chapter and substitute the values established in the previous step, keeping the original constraint in view.

Use the simplified expression to isolate the unknown, then plug the result back into the question setup to confirm the working is internally consistent.

Cross-check against a boundary or limiting case. Both the dimensional balance and the qualitative behaviour at the extreme should agree with the candidate answer.

Combine the steps above to identify the correct option. The remaining choices each fail at least one of the consistency, dimensional, or boundary checks.

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