What is the factorisation of ( 121-4y^2 )?
Answer and explanation
Correct answer: \((11+2y)(11-2y)\)
The expression is a difference of two squares: \(121=11^2\) and \(4y^2=(2y)^2\). Using \(a^2-b^2=(a+b)(a-b)\), we get \(121-4y^2=(11+2y)(11-2y)\). The option \((11-2y)^2\) would also produce a middle term \(-44y\), so it is not correct. Exam tip: identify the square roots of both terms before applying the difference-of-squares identity.
Frequently asked questions
What is the correct answer to this question?
\((11+2y)(11-2y)\)
Why is this the correct answer?
The expression is a difference of two squares: \(121=11^2\) and \(4y^2=(2y)^2\). Using \(a^2-b^2=(a+b)(a-b)\), we get \(121-4y^2=(11+2y)(11-2y)\). The option \((11-2y)^2\) would also produce a middle term \(-44y\), so it is not correct. Exam tip: identify the square roots of both terms before applying the difference-of-squares identity.
Which subject and chapter does this question cover?
This is a Class 9 Mathematics question. Chapter: Exploring Algebraic Identities. Topic: Algebraic identities.
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