Write whether the following statements are true or false. Justify your answers.
Every quadratic equation has exactly one root.
To do:
We have to find whether the given statements are true or false.
Solution:
(i) We know that,
A quadratic equation has two roots.
For example,
$x^2-16=0$ has two distinct roots $-4$ and $4$.
Hence, the given statement is false.
(ii) We know that,
A quadratic equation has two roots(real or imaginary).
For example,
$x^2+9=0$ has no real roots.
Hence, the given statement is false.
(iii) We know that,
A quadratic equation has two and only two roots(real or imaginary).
Hence, the given statement is false.
(iv) We know that,
A quadratic equation has two roots(real or imaginary).
Hence, the given statement is true.
(v) In a quadratic equation $ax^2+bx+c = 0$, if $a$ and $c$ have opposite signs, then $ac<0$
This implies,
$D=b^2 – 4ac > 0$
The discriminant is always positive, so it always has real roots.
Hence, the given statement is true.
(vi) In a quadratic equation $ax^2+bx+c = 0$, if $a$ and $c$ have same signs, then $ac>0$
This implies,
$D=(0)^2 - 4ac$
$=-4ac<0$
The discriminant is always negative, so it has no real roots.
Hence, the given statement is true.
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