Đáp án:
a)$\frac{1}{3}$ - $\frac{3}{5}$ + $\frac{5}{7}$ - $\frac{7}{9}$ + $\frac{9}{11}$ - $\frac{11}{13}$ + $\frac{13}{15}$ - $\frac{1}{3}$ + $\frac{3}{5}$ - $\frac{5}{7}$ + $\frac{7}{9}$ - $\frac{9}{11}$ + $\frac{11}{13}$=$\frac{13}{15}$
b)$\frac{1}{9.10}$ - $\frac{1}{8.9}$ - .... - $\frac{1}{2.3}$ + $\frac{1}{1.2}$ =$-\frac{9}{10}$
Giải thích các bước giải:
a)$\frac{1}{3}$ - $\frac{3}{5}$ + $\frac{5}{7}$ - $\frac{7}{9}$ + $\frac{9}{11}$ - $\frac{11}{13}$ + $\frac{13}{15}$ - $\frac{1}{3}$ + $\frac{3}{5}$ - $\frac{5}{7}$ + $\frac{7}{9}$ - $\frac{9}{11}$ + $\frac{11}{13}$
= ($\frac{1}{3}$ - $\frac{1}{3}$) + (-$\frac{3}{5}$ + $\frac{3}{5}$) + ($\frac{5}{7}$ - $\frac{5}{7}$) + (-$\frac{7}{9}$ + $\frac{7}{9}$) + ($\frac{9}{11}$ - $\frac{9}{11}$) + (-$\frac{11}{13}$ + $\frac{11}{13}$) + $\frac{13}{15}$
=$\frac{13}{15}$
b)$\frac{1}{9.10}$ - $\frac{1}{8.9}$ - .... - $\frac{1}{2.3}$ + $\frac{1}{1.2}$
= $\frac{1}{10}$.$\frac{1}{9}$- $\frac{1}{8}$. $\frac{1}{9}$ -....-$\frac{1}{3}$.$\frac{1}{2}$- $\frac{1}{2}$.1
=$\frac{1}{10}$-$1$
=$-\frac{9}{10}$
Cho mk ctlhn nha
Chúc bạn học tốt ^-^
