Giải bài 7 trang 31

Đề bài

Rút gọn về phân số tối giản:

a) $\frac{-147}{252}$

b) $\frac{765}{900}$

c) $\frac{11.3-11.8}{17-6}$

d) $\frac{3^5{.2}^4}{{8.3}^6}$

e) $\frac{84.45}{49.54}$

Lời giải chi tiết

a) $\frac{-147}{252}=\frac{-147:21}{252:21}=\frac{-7}{12}$

b) $\frac{765}{900}=\frac{765:45}{900:45}=\frac{17}{20}$

c) $\frac{11.3-11.8}{17-6}=\frac{11.(3-8)}{11}=\frac{11.(-5)}{11}=-5$

d) $\frac{3^5{.2}^4}{{8.3}^6}=\frac{3^5{.2}^4}{3^6{.2}^3}=\frac{3^5{.2}^4:\left(3^5{.2}^3\right)}{3^6{.2}^3:\left(3^5{.2}^3\right)}=\frac{3^{5-5}{.2}^{4-3}}{3^{6-5}{.2}^{3-3}}=\frac{3^0{.2}^1}{3^1{.2}^0}=\frac{2}{3}$

e) $\frac{84.45}{49.54}=\frac{2^2{.3.7.3}^2.5}{7^2{.2.3}^3}=\frac{2^2{.3}^3.5.7}{{2.3}^3{.7}^2}=\frac{2.5}{7}=\frac{10}{7}$