Rectangle with diagonal 6 cm, diagonal makes 30° with a side — area In a rectangle, the diagonal has length 6 cm and makes a 30° angle with one side. Find the area of the rectangle.

Difficulty: Easy

Correct Answer: 9 √3 cm2

Explanation:


Introduction / Context:
Knowing the diagonal and its angle with a side determines both side lengths via basic trigonometry, from which the area follows directly.


Given Data / Assumptions:

  • Diagonal d = 6 cm.
  • Let sides be a (adjacent to the 30°) and b (opposite).
  • Angle between diagonal and side a = 30°.


Concept / Approach:
tan 30° = b/a = 1/√3 ⇒ b = a/√3. Also, d² = a² + b². Substitute b and solve for a, then compute area A = a·b.


Step-by-Step Solution:

b = a/√3d² = a² + b² = a² + a²/3 = (4/3)a²6² = (4/3)a² ⇒ a² = 27 ⇒ a = 3√3, b = 3Area A = a·b = 3√3 · 3 = 9√3 cm²


Verification / Alternative check:
Compute diagonal from a and b: √(27 + 9) = √36 = 6 (consistent).


Why Other Options Are Wrong:
9 cm² corresponds to b = 3 with a = 3, which would make tan 30° = 1; 27 and 36 cm² are incompatible with d = 6.


Common Pitfalls:
Using sin or cos instead of tan to relate a and b at the specified angle.


Final Answer:
9 √3 cm2

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