Roots?

Algebra Level 4

If a , b a,b and c c are positive odd numbers, then what can we say about the equation a x 2 + b x + c = 0 ax^2+bx+c= 0 ?

Has Odd Positive Roots None Of The Above Has Integer Roots Doesn't Have Rational Roots

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2 solutions

Otávio Augusto
Feb 8, 2016

Let x 1 x_ 1 and x 2 x_ 2 be the roots of the equation.

We know that x 1 x_ 1 and x 2 x_ 2 must satisfy the statements below:

x 1 + x 2 = o d d x_1 + x_2 = -odd . This is only possible if: x 1 = e v e n x_1 = even and x 2 = o d d x_2 = odd .

x 1 x 2 = o d d x_1 x_2 = odd . This is only possible if: x 1 = o d d x_1 = odd and x 2 = o d d x_2 = odd .

As there's no integer or rational numbers that satisfy both conditions, we can say that the equation doesn't have rational roots.

Nice Soln. :)

Aditya Narayan Sharma - 5 years, 4 months ago
Tom Engelsman
Feb 24, 2017

Let x = p q x = \frac{p}{q} be a rational root to the above quadratic equation. This computes to:

a ( p q ) 2 + b ( p q ) + c = 0 a p 2 + b p q + c q 2 = 0 a(\frac{p}{q})^{2} + b(\frac{p}{q}) + c = 0 \Rightarrow ap^2 + bpq + cq^2 = 0

If p , q p,q are both odd, then we obtain odd + odd + odd \neq 0. If p is odd(even) and q is even(odd), then we obtain even + even + odd \neq 0. Hence, we only obtain odd integer solutions in both cases so no rational root solutions exist.

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