Question

Find $ab$, if $a+b=\sqrt{11},a^2+b^2=5$

Answer 1

As we know that,

${(a+b)}^2=a^2+b^2+2ab$

Given:-

$a+b=\sqrt{11}$

$a^2+b^2=5$

Therefore,

${(a+b)}^2=(a^2+b^2)+2ab$

$\Rightarrow {\left(\sqrt{11}\right)}^2=5+2ab$

$ab=\frac{11-5}{2}=3$