Step-by-step explanation:
[tex]area \: of \: a \: triangle = \frac{1}{2} \times base \times height \\ \\ base = \frac{a}{2} cm \\ {h}^{2} + {( \frac{a}{2} )}^{2} = {a}^{2} \\ \\ h = \sqrt{ {a}^{2} - \frac{ {a}^{2} }{4} } \\ \\ area \: of \: triangle = \frac{1}{2} \times b \times h \\ = \frac{1}{2} \times \frac{a}{2} \times \sqrt{ {a}^{2} - \frac{ {a}^{2} }{4} } \\ \\ = \frac{a}{4} \times \sqrt{ {a}^{2} - \frac{ {a}^{2} }{4} } [/tex]
