It is given that the difference between the zeroes of $4 x^{2}-8 k x+9$ is 4 and $k>0$. Then, $k=$ ?
(a) $\frac{1}{2}$
(b) $\frac{3}{2}$
(c) $\frac{5}{2}$
(d) $\frac{7}{2}$
(c) $\frac{5}{2}$
Let the zeroes of the polynomial be $\alpha$ and $\alpha+4$.
Here, $p(x)=4 x^{2}-8 k x+9$
Comparing the given polynomial with $a x^{2}+b x+c$, we get:
$a=4, b=-8 k$ and $c=9$
Now, sum of the roots $=-\frac{b}{a}$
$=>\alpha+\alpha+4=\frac{-(-8 k)}{4}$
$=>2 \alpha+4=2 k$
$=>\alpha+2=k$
$=>\alpha=(k-2) \quad \ldots(\mathrm{i})$
Also, product of the roots, $\alpha \beta=\frac{c}{a}$
$=>\alpha(\alpha+4)=\frac{9}{4}$
$=>(k-2)(k-2+4)=\frac{9}{4}$
$=>(k-2)(k+2)=\frac{9}{4}$
$=>k^{2}-4=\frac{9}{4}$
$=>4 k^{2}-16=9$
$=>4 k^{2}=25$
$=>k^{2}=\frac{25}{4}$
$=>k=\frac{5}{2} \quad(\because k>0)$