What Is the Probability of No Real Roots in a Quadratic Equation?

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The discussion centers on calculating the probability that the quadratic equation x^2 + ax + b = 0 has no real roots when a and b are randomly selected from the interval [0, 2]. The key condition for the equation to lack real roots is that the discriminant, given by a^2 - 4b, must be less than zero. Participants are encouraged to share their attempts and specific challenges to facilitate assistance. The conversation emphasizes collaborative problem-solving in understanding the mathematical concepts involved. Engaging with the problem can lead to a clearer grasp of quadratic equations and their properties.
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Homework Statement


Given an interval [0,2], randomly select two numbers a, b in it. What is the probability of the situation where the equation x^2+ax+b=0 has no real root?

Homework Equations





The Attempt at a Solution

 
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Hi yuqiao! :smile:

(try using the X2 tag just above the Reply box :wink:)

Show us what you've tried, and where you're stuck, and then we'll know how to help! :smile:
 
I tried to combine those 2 formulas but it didn't work. I tried using another case where there are 2 red balls and 2 blue balls only so when combining the formula I got ##\frac{(4-1)!}{2!2!}=\frac{3}{2}## which does not make sense. Is there any formula to calculate cyclic permutation of identical objects or I have to do it by listing all the possibilities? Thanks
Since ##px^9+q## is the factor, then ##x^9=\frac{-q}{p}## will be one of the roots. Let ##f(x)=27x^{18}+bx^9+70##, then: $$27\left(\frac{-q}{p}\right)^2+b\left(\frac{-q}{p}\right)+70=0$$ $$b=27 \frac{q}{p}+70 \frac{p}{q}$$ $$b=\frac{27q^2+70p^2}{pq}$$ From this expression, it looks like there is no greatest value of ##b## because increasing the value of ##p## and ##q## will also increase the value of ##b##. How to find the greatest value of ##b##? Thanks
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