If a , b and c are positive odd numbers, then what can we say about the equation a x 2 + b x + c = 0 ?
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Let x = q p be a rational root to the above quadratic equation. This computes to:
a ( q p ) 2 + b ( q p ) + c = 0 ⇒ a p 2 + b p q + c q 2 = 0
If p , q are both odd, then we obtain odd + odd + odd = 0. If p is odd(even) and q is even(odd), then we obtain even + even + odd = 0. Hence, we only obtain odd integer solutions in both cases so no rational root solutions exist.
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Let x 1 and x 2 be the roots of the equation.
We know that x 1 and x 2 must satisfy the statements below:
x 1 + x 2 = − o d d . This is only possible if: x 1 = e v e n and x 2 = o d d .
x 1 x 2 = o d d . This is only possible if: x 1 = o d d and x 2 = o d d .
As there's no integer or rational numbers that satisfy both conditions, we can say that the equation doesn't have rational roots.