Difficulty: Medium
Correct Answer: 336
Explanation:
Introduction / Context:For a parallelogram, area = a*b*sin(θ). A diagonal along with side lengths can determine the included angle using the cosine rule for parallelogram diagonals.
Given Data / Assumptions:
Concept / Approach:Diagonal formula: d^2 = a^2 + b^2 + 2ab*cosθ. Solve for cosθ, then compute sinθ and area = a*b*sinθ.
Step-by-Step Solution:
40^2 = 30^2 + 14^2 + 2*30*14*cosθ1600 = 900 + 196 + 840*cosθ ⇒ 1600 − 1096 = 840*cosθ504 = 840*cosθ ⇒ cosθ = 0.6 ⇒ sinθ = 0.8.Area = a*b*sinθ = 30*14*0.8 = 336 m^2.Verification / Alternative check:Use identity d1^2 + d2^2 = 2(a^2 + b^2) to cross-check angle consistency (optional).
Why Other Options Are Wrong:136, 236, 436 do not match the area from the uniquely determined angle.
Common Pitfalls:Using 0.5*a*b*sinθ (triangle formula) by mistake; a parallelogram’s area is a*b*sinθ.
Final Answer:336
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