Question Number 110728 by Study last updated on 30/Aug/20
$${a}+{b}=\mathrm{9}\:\:,\:\:{ab}=\mathrm{20}\:\:\:\:\:{a}−{b}=? \\ $$
Answered by som(math1967) last updated on 30/Aug/20
$$\left(\mathrm{a}−\mathrm{b}\right)^{\mathrm{2}} =\left(\mathrm{a}+\mathrm{b}\right)^{\mathrm{2}} −\mathrm{4ab} \\ $$$$\left(\mathrm{a}−\mathrm{b}\right)^{\mathrm{2}} =\mathrm{81}−\mathrm{80} \\ $$$$\Rightarrow\left(\mathrm{a}−\mathrm{b}\right)=\pm\mathrm{1} \\ $$