Đáp án:

a $\frac{54}{-90}$ =$\frac{54:18}{-90:18}$ =$\frac{4}{9}$ $\frac{3}{-5}$

c, $\frac{-39}{91}$ =$\frac{-39:13}{91:13}$ =$\frac{-3}{7}$ 

d, $\frac{17.2-13.17}{11.2-11.19}$ = $\frac{17(2-13)}{11(2-19)}$=$\frac{17.(-11)}{11.(-17)}$ =$\frac{-187}{-187}$ =1

b$\frac{-60}{-135}$ =$\frac{-60:15}{-135:15}$ =$\frac{4}{9}$