(4/5-3/4)•(3/4-4/5)= (3,42-3/4):(4/5+4,3)=

А) ( $\frac{4}{5} - \frac{3}{4}$ ) × ( $\frac{3}{4} - \frac{4}{5}$ ) = ( $\frac{16-15}{20}$ ) ×( $\frac{15-16}{20}$ ) = $\frac{1}{20}$ × (- $\frac{1}{20}$ ) = - $\frac{1}{400}$
б) (3,42-3/4):(4/5+4,3)= (3 $\frac{42}{100}$ - $\frac{3}{4}$ ) : ( $\frac{4}{5}$ + 4 $\frac{3}{10}$ ) = ( $\frac{342}{100}$ - $\frac{3}{4}$ ) : ( $\frac{4}{5} + \frac{43}{10}$ ) = ( $\frac{342-75}{100}$ ) : ( $\frac{8+43}{10}$ ) = $\frac{267}{100} : \frac{51}{10}$ = $\frac{267}{100} * \frac{10}{51}$ = $\frac{89}{170}$ ≈ 0,5