Question 329432
Diagonal:
{{{D^2=L^2+W^2=15^2}}}
.
.
Perimeter:
{{{2(L+W)=42}}}
{{{L+W=21}}}
.
.
Area:
{{{A=LW}}}
.
.
.
{{{(L+W)^2=L^2+2LW+W^2}}}
{{{(L+W)^2=(L^2+W^2)+2LW}}}
{{{21^2=15^2+2A}}}
{{{2A=21^2-15^2}}}
{{{A=(1/2)(21^2-15^2)}}}
{{{A=(1/2)(441-225)}}}
{{{A=(1/2)(216)}}}
{{{A=108}}}