Rút gọn rồi quy đồng mẫu số các phân số sau: A = 2002 / 2000.16 - 1970

* Hướng dẫn giải

$A=\frac{2002}{2000.16-1970}=\frac{2002}{(2002-2).16-1970}$$=\frac{2002}{2002.(16-1)}=\frac{1}{15}$

và $B=\frac{12.3+\mathrm{2.4.6}+\mathrm{4.8.12}+\mathrm{7.14.21}}{\mathrm{1.3.6}+\mathrm{2.6.12}+\mathrm{4.12.24}+\mathrm{7.21.42}}$$=\frac{12.3+\mathrm{2.4.6}+\mathrm{4.8.12}+\mathrm{7.14.21}}{\mathrm{1.3.2.3}+\mathrm{2.6.3.4}+\mathrm{4.12.3.8}+\mathrm{7.21.14.3}}$$=\frac{12.3+\mathrm{2.4.6}+\mathrm{4.8.12}+\mathrm{7.14.21}}{3.(12.3+\mathrm{2.4.6}+\mathrm{4.8.12}+\mathrm{7.14.21})}=\frac{1}{3}=\frac{5}{15}$

Vậy B > A