a)1/2-1/3.7-1/7.11-1/11.15-1/15.19-1/19.23-1/23.27
b)1-1/5.10-1/10.15-1/15.20-…-1/95.100
c)x+(31/12)²=(-42/12)²-x=y²
a)1/2-1/3.7-1/7.11-1/11.15-1/15.19-1/19.23-1/23.27
b)1-1/5.10-1/10.15-1/15.20-…-1/95.100
c)x+(31/12)²=(-42/12)²-x=y²
Giải thích các bước giải:
a, = $\frac{1}{2}$ -($\frac{1}{3.7}$ + $\frac{1}{7.11}$ + … + $\frac{1}{23.27}$ )
= $\frac{1}{2}$- $\frac{1}{4}$.($\frac{1}{3}$- $\frac{1}{7}$+ $\frac{1}{7}$ -…-$\frac{1}{27}$ )
=$\frac{1}{2}$- $\frac{1}{4}$.$\frac{8}{27}$
=$\frac{23}{54}$
b,=$\frac{1}{5}$ .($\frac{5}{5.10}$ -$\frac{5}{10.15}$ -…-$\frac{5}{95.100}$ )
= $\frac{1}{5}$.($\frac{1}{5}$ – $\frac{1}{10}$ +$\frac{1}{10}$ -..-$\frac{1}{100}$ )
= $\frac{1}{5}$.$\frac{19}{100}$=$\frac{19}{500}$