What expression is x^2-20x+100 equal to?
Answer and explanation
Correct answer: (x-10)^2
Using the perfect-square identity (a-b)^2=a^2-2ab+b^2, we get x^2-20x+100=x^2-2\cdot x\cdot10+10^2=(x-10)^2. Option B would produce a middle term of +20x, so it is incorrect. Exam tip: take the square roots of the first and last terms and check whether twice their product matches the middle term.
Frequently asked questions
What is the correct answer to this question?
(x-10)^2
Why is this the correct answer?
Using the perfect-square identity (a-b)^2=a^2-2ab+b^2, we get x^2-20x+100=x^2-2\cdot x\cdot10+10^2=(x-10)^2. Option B would produce a middle term of +20x, so it is incorrect. Exam tip: take the square roots of the first and last terms and check whether twice their product matches the middle term.
Which subject and chapter does this question cover?
This is a Class 10 Mathematics question. Chapter: Polynomials. Topic: Operations on real numbers and the laws of exponents.
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