A rectangle model has sides (x+9) and (x-1). Which area is correct?
Answer and explanation
Correct answer: \(x^2+8x-9\)
The area of a rectangle is the product of its side lengths: \((x+9)(x-1)=x^2-x+9x-9=x^2+8x-9\). Therefore, the correct area is \(x^2+8x-9\). In option A, the middle terms have been combined with incorrect signs. Exam tip: after multiplying, carefully combine like terms such as \(-x\) and \(9x\).
Frequently asked questions
What is the correct answer to this question?
\(x^2+8x-9\)
Why is this the correct answer?
The area of a rectangle is the product of its side lengths: \((x+9)(x-1)=x^2-x+9x-9=x^2+8x-9\). Therefore, the correct area is \(x^2+8x-9\). In option A, the middle terms have been combined with incorrect signs. Exam tip: after multiplying, carefully combine like terms such as \(-x\) and \(9x\).
Which subject and chapter does this question cover?
This is a Class 9 Mathematics question. Chapter: Exploring Algebraic Identities. Topic: Visual models of identities.
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