For each of the following, find a quadratic polynomial whose sum and product respectively of the zeroes are as given. Also, find the zeroes of these
polynomials by factorisation.
(i) $\frac{-8}{3}, \frac{4}{3}$
(ii) $\frac{21}{8}, \frac{5}{16}$
(iii) $-2 \sqrt{3},-9$
(iv) $\frac{-3}{2 \sqrt{5}},-\frac{1}{2}$
(i) Given that, sum of zeroes $(S)=-\frac{8}{3}$
and product of zeroes $(P)=\frac{4}{3}$
$\therefore$ Required quadratic expression, $f(x)=x^{2}-S x+P$
$=x^{2}+\frac{8}{3} x+\frac{4}{3}=3 x^{2}+8 x+4$
Using factorisation method, $=3 x^{2}+6 x+2 x+4$
$=3 x(x+2)+2(x+2)=(x+2)(3 x+2)$
Hence, the zeroes of $f(x)$ are $-2$ and $-\frac{2}{3}$.
(ii) Given that, $S=\frac{21}{8}$ and $P=\frac{5}{16}$
$\therefore$ Required quadratic expression, $f(x)=x^{2}-S x+P$
$=x^{2}-\frac{21}{8} x+\frac{5}{16}=16 x^{2}-42 x+5$
Using factorisation method $=16 x^{2}-40 x-2 x+5$
$=8 x(2 x-5)-1(2 x-5)=(2 x-5)(8 x-1)$
Hence, the zeroes of $f(x)$ are $\frac{5}{2}$ and $\frac{1}{8}$
(iii) Given that, $S=-2 \sqrt{3}$ and $P=-9$
$\therefore$ Required quadratic expression,
$f(x)=x^{2}-S x+P=x^{2}+2 \sqrt{3} x-9$
$=x^{2}+3 \sqrt{3} x-\sqrt{3} x-9$ [using factorisation method]
$=x(x+3 \sqrt{3})-\sqrt{3}(x+3 \sqrt{3})$
$=(x+3 \sqrt{3})(x-\sqrt{3})$
Hence, the zeroes of $f(x)$ are $-3 \sqrt{3}$ and $\sqrt{3}$.
(iv) Given that, $S=-\frac{3}{2 \sqrt{5}}$ and $P=-\frac{1}{2}$
$\therefore$ Required quadratic expression,
$f(x)=x^{2}-S x+P=x^{2}+\frac{3}{2 \sqrt{5}} x-\frac{1}{2}$
$=2 \sqrt{5} x^{2}+3 x-\sqrt{5}$
Using factorisation method, $=2 \sqrt{5} x^{2}+5 x-2 x-\sqrt{5}$
$=\sqrt{5} x(2 x+\sqrt{5})-7(2 x+\sqrt{5})$
$=(2 x+\sqrt{5})(\sqrt{5} x-1)$
Hence,the zeroes of $f(x)$ are $-\frac{\sqrt{5}}{2}$ and $\frac{1}{\sqrt{5}}$