Rectangle from diagonal and perimeter:\nThe diagonal of a rectangle is 17 cm and its perimeter is 46 cm. Find the area (in sq. cm).

Difficulty: Medium

Correct Answer: 120

Explanation:


Introduction / Context:
This problem combines Pythagoras with perimeter relations to determine a rectangle’s area from diagonal and perimeter.


Given Data / Assumptions:

  • Sides a, b (cm).
  • Diagonal d = 17 cm so a^2 + b^2 = 17^2 = 289.
  • Perimeter P = 46 cm ⇒ a + b = 23.


Concept / Approach:
Use identity (a + b)^2 = a^2 + b^2 + 2ab to find ab, which equals the area for rectangles.


Step-by-Step Solution:

(a + b)^2 = 23^2 = 529.a^2 + b^2 = 289.So 529 = 289 + 2ab ⇒ 2ab = 240 ⇒ ab = 120.Area = a*b = 120 sq. cm.


Verification / Alternative check:
If a = 8 and b = 15, then diagonal √(64+225)=√289=17 and perimeter 2*(8+15)=46; area 120 checks out.


Why Other Options Are Wrong:
110, 130, 140 do not satisfy both the diagonal and perimeter constraints simultaneously.


Common Pitfalls:
Trying to solve for individual a and b first; area can be obtained directly from the identity without explicit a, b values.


Final Answer:
120

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