Max Magnitude of a,b,c in Quaratic Equation |ax^2+bx+c|<=1

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SUMMARY

The discussion focuses on determining the maximum magnitude of coefficients a, b, and c in the quadratic equation |ax² + bx + c| ≤ 1 for all x in the interval [0, 1]. The initial analysis reveals that setting x = 0 leads to |c| ≤ 1, establishing that the maximum magnitude of c is 1. Further exploration indicates that the coefficients a and b cannot be independently constrained; instead, their values are interdependent based on the behavior of the quadratic function within the defined bounds. The key insight is that the entire curve must remain within the box defined by x = 0, x = 1, y = -1, and y = 1.

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Homework Statement



[tex]|ax^{2}+bx+c|\leq1 \forall x\in[0,1][/tex]
Find the maximum magnitude of a,b, and c possible!

My attempt:
putting x=0;
|c|<=1
hence its maximummagnitude is 1.
Help me with a and b.
regards,
Ritwik
 
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You aren't going to be able to set limits on the coefficients separately, I think. You are probably going to have relationships between the coefficients.

Picture it this way. The inequality is saying that

[tex] -1 \leq ax^{2}+bx+c \leq 1[/tex] for [tex]0 \leq x \leq 1[/tex].

So a portion of the curve for this function has to fit entirely in the "box" bounded by x = 0, x = 1, y = -1, and y = 1. (Obviously, the parabola goes on forever elsewhere...) What does that mean for intersection points of the parabola with the "box"? How might you find coefficients from that?
 

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