Choose the correct result of ( (z+9)(z-9) ).
Answer and explanation
Correct answer: \(z^2-81\)
This expression uses the identity \((a+b)(a-b)=a^2-b^2\). Taking \(a=z\) and \(b=9\), \((z+9)(z-9)=z^2-9^2=z^2-81\). \(z^2+81\) is incorrect because this is a difference of squares, not a sum. Exam tip: for binomials with opposite signs, the middle terms cancel.
Frequently asked questions
What is the correct answer to this question?
\(z^2-81\)
Why is this the correct answer?
This expression uses the identity \((a+b)(a-b)=a^2-b^2\). Taking \(a=z\) and \(b=9\), \((z+9)(z-9)=z^2-9^2=z^2-81\). \(z^2+81\) is incorrect because this is a difference of squares, not a sum. Exam tip: for binomials with opposite signs, the middle terms cancel.
Which subject and chapter does this question cover?
This is a Class 9 Mathematics question. Chapter: Exploring Algebraic Identities. Topic: Algebraic identities.
Student feedback
Was this question useful?
👍 0 Helpful 👎 0 Not helpful
Yes 0% No 0%
0 responsesStudent Reviews
No published reviews yet.
