Nilai x yang memenuhi ..................................

[tex]( ( \frac{2}{5}) ^x * ( \frac{2}{5}) ^2 )^3 = ( \frac{25}{4} )^{21} [/tex]

[tex]( ( \frac{2}{5}) ^ {(x+2)*3} = ( \frac{25}{4} )^{21} [/tex]

[tex]( ( \frac{2}{5}) ^ {(3x+6)} = ( \frac{5^2}{2^2} )^{21} [/tex]

[tex]( ( \frac{2}{5}) ^ {(3x+6)} = ( \frac{2^2}{5^2} )^{-21} [/tex]

[tex]( ( \frac{2}{5}) ^ {(3x+6)} = ( \frac{2}{5} )^{-42} [/tex]

dikeluarkan 

3x+6 = -42
3x = -48

x = -16