A=1/10+1/15+1/21+…+1/66 m.n giải nhanh giúp mình nha 07/10/2021 Bởi Ruby A=1/10+1/15+1/21+…+1/66 m.n giải nhanh giúp mình nha
A=1/10+1/15+1/21+…+1/66 =>1/2A =1/20+1/30+1/42+…+1/132 =>1/2A =1/4.5+1/5.6+1/6.7+…+1/11.12 =>1/2A =1/4-1/5+1/5-1/6+1/6-1/7+…+1/11-1/12 =>1/2A =1/4-1/12 => A =1/2-1/6 => A = 1/3 Bình luận
Đáp án: A = $\frac{1}{10}$ + $\frac{1}{15}$ + $\frac{1}{21}$ + …. + $\frac{1}{55}$ + $\frac{1}{66}$ A = 2 ( $\frac{1}{20}$ + $\frac{1}{30}$ + $\frac{1}{42}$ + $\frac{1}{56}$ + $\frac{1}{72}$ + $\frac{1}{90}$ + $\frac{1}{110}$ + $\frac{1}{132}$ ) A = 2 ( $\frac{1}{4.5}$ + $\frac{1}{5.6}$ + $\frac{1}{6.7}$ + $\frac{1}{7.8}$ + $\frac{1}{8.9}$ + $\frac{1}{9.10}$ + $\frac{1}{10.11}$ ) A = 2 [( $\frac{1}{4}$ – $\frac{1}{5}$ ) + ( $\frac{1}{5}$ – $\frac{1}{6}$ ) + ( $\frac{1}{6}$ – $\frac{1}{7}$ ) + ( $\frac{1}{7}$ – $\frac{1}{8}$ ) + ( $\frac{1}{8}$ – $\frac{1}{9}$ ) + ( $\frac{1}{9}$ – $\frac{1}{10}$ ) + ( $\frac{1}{10}$ – $\frac{1}{11}$ )] A = 2 ( $\frac{1}{4}$ – $\frac{1}{12}$ ) ⇒ A = $\frac{1}{3}$ Bình luận
A=1/10+1/15+1/21+…+1/66
=>1/2A =1/20+1/30+1/42+…+1/132
=>1/2A =1/4.5+1/5.6+1/6.7+…+1/11.12
=>1/2A =1/4-1/5+1/5-1/6+1/6-1/7+…+1/11-1/12
=>1/2A =1/4-1/12
=> A =1/2-1/6
=> A = 1/3
Đáp án:
A = $\frac{1}{10}$ + $\frac{1}{15}$ + $\frac{1}{21}$ + …. + $\frac{1}{55}$ + $\frac{1}{66}$
A = 2 ( $\frac{1}{20}$ + $\frac{1}{30}$ + $\frac{1}{42}$ + $\frac{1}{56}$ + $\frac{1}{72}$ + $\frac{1}{90}$ + $\frac{1}{110}$ + $\frac{1}{132}$ )
A = 2 ( $\frac{1}{4.5}$ + $\frac{1}{5.6}$ + $\frac{1}{6.7}$ + $\frac{1}{7.8}$ + $\frac{1}{8.9}$ + $\frac{1}{9.10}$ + $\frac{1}{10.11}$ )
A = 2 [( $\frac{1}{4}$ – $\frac{1}{5}$ ) + ( $\frac{1}{5}$ – $\frac{1}{6}$ ) + ( $\frac{1}{6}$ – $\frac{1}{7}$ ) + ( $\frac{1}{7}$ – $\frac{1}{8}$ ) + ( $\frac{1}{8}$ – $\frac{1}{9}$ ) + ( $\frac{1}{9}$ – $\frac{1}{10}$ ) + ( $\frac{1}{10}$ – $\frac{1}{11}$ )]
A = 2 ( $\frac{1}{4}$ – $\frac{1}{12}$ )
⇒ A = $\frac{1}{3}$