What is the discriminant \(D\) of the equation \(4x^2-8x-1=0\)?
Answer and explanation
Correct answer: 80
For a quadratic equation \(ax^2+bx+c=0\), the discriminant is \(D=b^2-4ac\). Here, \(a=4\), \(b=-8\), and \(c=-1\), so \(D=(-8)^2-4(4)(-1)=64+16=80\). The value 48 results from incorrectly treating the contribution of \(-4ac\) as negative. Exam tip: when \(c\) is negative, \(-4ac\) contributes a positive value.
Frequently asked questions
What is the correct answer to this question?
80
Why is this the correct answer?
For a quadratic equation \(ax^2+bx+c=0\), the discriminant is \(D=b^2-4ac\). Here, \(a=4\), \(b=-8\), and \(c=-1\), so \(D=(-8)^2-4(4)(-1)=64+16=80\). The value 48 results from incorrectly treating the contribution of \(-4ac\) as negative. Exam tip: when \(c\) is negative, \(-4ac\) contributes a positive value.
Which subject and chapter does this question cover?
This is a Class 10 Mathematics question. Chapter: Quadratic Equations. Topic: Methods of Solving Quadratic Equations.
Student feedback
Was this question useful?
👍 0 Helpful 👎 0 Not helpful
Yes 0% No 0%
0 responsesStudent Reviews
No published reviews yet.
