Help with simple linear algebra/quadratic equation proof

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The discussion centers on proving that if the quadratic equation ax² + bx + c = 0 holds for all x, then the coefficients must satisfy a = b = c = 0. Participants suggest substituting specific values for x, such as 0, 1, and -1, to generate a system of equations. This method effectively demonstrates that the only solution is when all coefficients are zero, confirming the proof. The approach emphasizes the utility of substituting values in polynomial equations to derive necessary conditions for coefficients.

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Q: Show that if ax^2 + bx + c = 0 for all x, then a=b=c=0

Please help, I'm just starting out in Linear Algebra and I'm not sure how to even start going about proving this. Thanks!
 
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drestupinblac said:
Q: Show that if ax^2 + bx + c = 0 for all x, then a=b=c=0

Please help, I'm just starting out in Linear Algebra and I'm not sure how to even start going about proving this. Thanks!
Welcome to Physics Forums!

If ax^2 + bx + c = 0 for all x, it's certainly true for, say, x = 0, x = 1, and x = -1. Substitute those values in your equation to get three equations in three unknowns, and solve for the three unknowns.
 
Thank you for the warm welcome :) The answer seems almost obvious now that I see it, I guess I didn't think it would be as easy as choosing values for x.
 

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