Jawabanmu

2014-05-07T14:17:46+07:00
s^2 + s^2 = d^2
2s^2 = d^2
2s^2 = 18^2 = 324
s^2 = 324/2 = 162
luas = s^2 = 162 cm^2
Jadi, luas persegi yaitu 162 cm^2
1 3 1
2014-05-07T14:23:53+07:00
Misalnya persegi ABCD
AC diagonalnya = 18 cm -> AB = BC, soalnya persegi.
Misal AB = y
Jadi AC^{2} = AB^{2} + BC^{2}

      AC^{2} =  y^{2} + y^{2}
      AC^{2} = 2 y^{2}
      18^{2} = 2 y^{2}
      324 = 2 y^{2}
       \frac{324}{2} = y^{2}
      162 = y^{2}
      y =  \sqrt{162}

Luas = s^{2}
        =  \sqrt{162^{2}
        = 162 cm^{2}
      
1 5 1