Cuboid from sum of edges and diagonal (rephrased) — compute surface area: The sum of the length, breadth, and height of a cuboid is 19 cm, and its space diagonal is 5√5 cm. What is the total surface area of the cuboid?

Difficulty: Medium

Correct Answer: 236 cm2

Explanation:


Introduction / Context:
Same setup as a classic identity problem: with l + b + h and the space diagonal known, compute the pairwise products and hence the total surface area.



Given Data / Assumptions:

  • l + b + h = 19 cm
  • d = 5√5 cm ⇒ d^2 = 125
  • Surface area S = 2(lb + bh + hl)


Concept / Approach:
Use (l + b + h)^2 = d^2 + 2(lb + bh + hl). Rearranging gives the sum of pairwise products directly.



Step-by-Step Solution:
(l + b + h)^2 − d^2 = 361 − 125 = 2362(lb + bh + hl) = 236 ⇒ S = 236 cm2



Verification / Alternative check:
Dimensions need not be individually determined; identity-based computation is sufficient.



Why Other Options Are Wrong:
361 and 125 are intermediate squares; “None” is unnecessary once identity is applied.



Common Pitfalls:
Forgetting to take 2 into account or mis-squaring 19.



Final Answer:
236 cm2

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