WAEC 2015 Mathematics · Question 15
The area of a rhombus is 110 cm. If the diagonals are 20 cm and (2x + 1) cm long, find the value of x.
Options
- A.5.0
- B.4.0
- C.3.0
- D.2.5
Answer: A. 5.0
Explanation written with AI and checked against the answer key
Analyze the question: We are given the area of a rhombus (110 cm²) and its two diagonals (20 cm and (2x + 1) cm). We need to find x. Concept: The area of a rhombus is half the product of its diagonals: Area = ½ × d₁ × d₂ Solution: 110 = ½ × 20 × (2x + 1) 110 = 10(2x + 1) 11 = 2x + 1 2x = 10 x = 5 Check: The second diagonal is 2(5) + 1 = 11 cm. Area = ½ × 20 × 11 = 110 cm². ✓ Answer: x = 5.0, which is option A. Tip: For any rhombus or kite, remember "half times diagonal times diagonal." Also, you can check your answer by substituting it back into the formula, which takes only a few seconds in the exam hall.AI can make mistakes. Report anything that looks wrong.
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