a=45 cm
b=53 cm
c=28cm
[tex]p = \frac{a + b + c}{2} = \frac{45 + 53 + 28}{2} = \frac{126}{2} = 63 [/tex]
Formula lui Heron:
[tex]A = \sqrt{p(p - a)(p - b)(p - c)} [/tex]
[tex] = \sqrt{63(63 - 45)(63 - 53)(63 - 28)} [/tex]
[tex] = \sqrt{63 \times 18 \times 10 \times 35} [/tex]
[tex] = \sqrt{396900} [/tex]
[tex] = 630 \: {cm}^{2} [/tex]