Advanced MathHardWidth of a rectangle from its diagonal
Advanced Math practice question
A rectangle has a diagonal of length 15, and its length is 3 more than its width. What is the width of the rectangle?
Answer: 9
w² + (w + 3)² = 225 gives 2w² + 6w − 216 = 0, so w² + 3w − 108 = 0 and (w + 12)(w − 9) = 0. The width is 9.
Common wrong answers
- If you answered 6
- 6 divides 15 by 3 and subtracts 1.
- If you answered 12
- 12 is the length, or the rejected root with its sign dropped.
- If you answered 15
- 15 is the diagonal.
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