Which equation is obtained when \((x-4)(x+9)=5x\) is written in standard form?
Answer and explanation
Correct answer: \(x^2-36=0\)
Expanding gives \((x-4)(x+9)=x^2+9x-4x-36=x^2+5x-36\). Now subtract \(5x\) from both sides: \(x^2+5x-36-5x=0\), so \(x^2-36=0\). Option B is only the expanded left-hand side and does not account for the \(5x\) on the right. Exam tip: To write a quadratic in standard form, bring all terms to one side and make the other side \(0\).
Frequently asked questions
What is the correct answer to this question?
\(x^2-36=0\)
Why is this the correct answer?
Expanding gives \((x-4)(x+9)=x^2+9x-4x-36=x^2+5x-36\). Now subtract \(5x\) from both sides: \(x^2+5x-36-5x=0\), so \(x^2-36=0\). Option B is only the expanded left-hand side and does not account for the \(5x\) on the right. Exam tip: To write a quadratic in standard form, bring all terms to one side and make the other side \(0\).
Which subject and chapter does this question cover?
This is a Class 10 Mathematics question. Chapter: Quadratic Equations. Topic: Introduction to Quadratic Equations.
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