Question 900676
2x+2y=20 and xy=21.
Just solve these simultaneous equations as a system.


Perimeter equation simplifies to x+y=10.


{{{y=10-x}}}
-
{{{x(10-x)=21}}}
{{{-x^2+10x-21=0}}}
{{{x^2-10x+21=0}}}
{{{(x+3)(x-7)=0}}}
The value for x that you must use is {{{highlight(x=7)}}}.
{{{y=10-7}}}
{{{highlight(y=3)}}}