Question 723563
X+Y=13
X=13-Y
XY=21
(13-Y)Y=21
13Y-Y^2=21
-Y^2+13Y-21=0
Y^2-13Y+21=0
{{{x = (-b +- sqrt( b^2-4*a*c ))/(2*a) }}}
X=(13+-SQRT(-13^2-4*1*21))/2*1
X=(13+-SQRT(169-94))/2
X=(13+-SQRT85)/2
X=(13+-9.22)/2
X=(13+9.22)/2 
X=22.22/2
X=11.11 ANS
X=(13-9.22)/2
X=3.78/2
X=1.89 ANS.