Rhombus with one angle 60° and shorter diagonal 8 cm: Find the area of the rhombus (in cm²).
-
A64√3 sq cm
-
B32√2 sq cm
-
C64√2 sq cm
-
D32√3 sq cm
-
ENone of these
Answer
Correct Answer: 32√3 sq cm
Explanation
Introduction / Context:A rhombus has all sides equal. Given one interior angle, the diagonals relate to the side and the angle. The area is a*b*sin(θ) where a and b are adjacent sides. With a known diagonal and angle, we can retrieve the side and compute area compactly.
Given Data / Assumptions:
- Interior angle θ = 60°.
- Shorter diagonal d_short = 8 cm.
- All sides equal to a.
Concept / Approach:For a rhombus with side a and angle θ: diagonals are a√(2 + 2cosθ) and a√(2 − 2cosθ). For θ = 60°, cosθ = 1/2. Then the two diagonals are a√3 and a. The shorter diagonal equals a, so a = 8 cm. Area = a^2 * sinθ = 8^2 * sin60° = 64 * (√3/2) = 32√3.
Step-by-Step Solution:
cos60° = 1/2 ⇒ diagonals: a√3 and a.Given d_short = 8 ⇒ a = 8.Area = a^2 * sin60° = 64 * (√3/2) = 32√3 cm².Verification / Alternative check:Rhombus area can also be (d1*d2)/2. Here d1 = a = 8; d2 = a√3 = 8√3 ⇒ area = (8 * 8√3)/2 = 32√3, consistent.
Why Other Options Are Wrong:Values with √2 arise from square/45° assumptions; 64√3 doubles the correct area.
Common Pitfalls:Confusing which diagonal is shorter at θ = 60°; it is a, not a√3.
Final Answer:32√3 sq cm