theo bài ra ta có:

\(\frac{3a^2-b^2}{a^2+b^2}=\frac{3}{4}\)

=> 4( 3a² - b²) = 3( a²+ b²)

=> 12a²- 4b² = 3a² + 3b²

=> 12a²- 3a² = 3b² + 4b²

=> 9a²= 7b²

=> \(\frac{7}{9}=\frac{a^2}{b^2}\Rightarrow\sqrt{\frac{7}{9}}=\frac{a}{b}\)

vậy \(\sqrt{\frac{7}{9}}=\frac{a}{b}\)

125 x 15 - 25 x15

= 15 x (125 - 25)

= 15 x 100

= 1500