Ta có:
` A = \frac{27^8 . 4^5}{2^{12} . 9^{11}} `
` = \frac{3^{24} . 2^{10}}{2^{12} . 3^{22}} `
` = \frac{3^2}{2^2} `
` = \frac{9}{4} `
` B = \frac{25^6 . 3^{15}}{9^7 . 5^{14}} `
` = \frac{5^{12} . 3^{15}}{3^{14} . 5^{14}} `
` = \frac{3}{5^2} `
` = \frac{3}{25} `
Vì ` 9/4 > 1 => A > 1 `
Mà ` 3/(25) < 1 => B < 1 `
` => A > B `
Vậy` A > B `