Which is the correct expansion of ( (5a-2b)^2 )?
Answer and explanation
Correct answer: \(25a^2-20ab+4b^2\)
Using \((x-y)^2=x^2-2xy+y^2\), take \(x=5a\) and \(y=2b\). Thus, \((5a-2b)^2=(5a)^2-2(5a)(2b)+(2b)^2=25a^2-20ab+4b^2\). Option B has a positive middle term, which belongs to \((x+y)^2\). Exam tip: square the complete first and last terms, and include \(-2\) in the middle term.
Frequently asked questions
What is the correct answer to this question?
\(25a^2-20ab+4b^2\)
Why is this the correct answer?
Using \((x-y)^2=x^2-2xy+y^2\), take \(x=5a\) and \(y=2b\). Thus, \((5a-2b)^2=(5a)^2-2(5a)(2b)+(2b)^2=25a^2-20ab+4b^2\). Option B has a positive middle term, which belongs to \((x+y)^2\). Exam tip: square the complete first and last terms, and include \(-2\) in the middle term.
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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