Question 799012
sides l and 2l
{{{ diagonal^2 = l^2 + 4*l^2 = 100 }}}
so {{{ 5*l^2 = 100 }}}
{{{ l^2 = 20 = 4*5}}}
and {{{ l = 2*sqrt(5) }}}
rectangle is {{{ 2*sqrt(5) }}} by {{{ 4*sqrt(5) }}}

{{{ diagonal=sqrt( (2*sqrt(5)*2*sqrt(5)) + (4*sqrt(5)*4*sqrt(5))) }}}
{{{ diagonal=sqrt((4*5) + (16*5) ) = sqrt(20+80) = sqrt(100) = 10 }}}