[tex]d = 18 \: cm[/tex]
[tex]d = l \sqrt{2} [/tex]
[tex]l \sqrt{2} = 18 \: | \div \sqrt{2} [/tex]
[tex]l = \frac{18}{ \sqrt{2} } [/tex]
[tex]l = \frac{18 \sqrt{2} }{2} [/tex]
[tex]l = 9 \sqrt{2} \: cm[/tex]
[tex]A = {l}^{2} [/tex]
[tex]A = {(9 \sqrt{2} )}^{2} [/tex]
[tex]A = 162 \: {cm}^{2} [/tex]
