P=(1/1*2+1/3.4+1/5.6+…+1/19.20):(1/11+1/12+…+1/20) 29/08/2021 Bởi Allison P=(1/1*2+1/3.4+1/5.6+…+1/19.20):(1/11+1/12+…+1/20)
Đáp án: Ta sẽ phân tích : 1/1.2 + 1/3.4 + 1/5.6 + …. + 1/19.20 = 1 – 1/2 + 1/3 – 1/4 + 1/5 – 1/6 + …. + 1/19 – 1/20 = ( 1 + 1/3 + 1/5 + … + 1/19) – ( 1/2 + 1/4 + 1/6 + …. + 1/20) = ( 1 + 1/2 + 1/3 + 1/4 + 1/5 + 1/6 + … + 1/19 + 1/20) – 2.( 1/2 + 1/4 + 1/6 + …. + 1/20) = ( 1 + 1/2 + 1/3 + 1/4 + 1/5 + 1/6 + … + 1/19 + 1/20 ) – (1+1/2+1/3+…+1/10) = 1/11 + … + 1/20 => P = ( 1/11 + … + 1/20) : ( 1/11+1/12+…+1/20) => P = 1 Giải thích các bước giải: Bình luận
$\frac{1}{2}$.2 + $\frac{1}{3}$ .4 + $\frac{1}{5}$ .6 + …. + $\frac{1}{19}$.20 = 1 – $\frac{1}{2}$ +$\frac{1}{3}$ – $\frac{1}{4}$ + $\frac{1}{5}$ – $\frac{1}{6}$ + …. + $\frac{1}{19}$ – $\frac{1}{20}$ = ( 1 + $\frac{1}{3}$ + $\frac{1}{5}$ + … + $\frac{1}{19}$ ) – ( $\frac{1}{2}$ + $\frac{1}{4}$ + $\frac{1}{6}$ + …. + $\frac{1}{20}$ ) = ( 1 + $\frac{1}{2}$ + $\frac{1}{3}$ + $\frac{1}{4}$ + $\frac{1}{5}$ + $\frac{1}{6}$ … + $\frac{1}{19}$ + $\frac{1}{20}$ ) – 2.( $\frac{1}{2}$ + $\frac{1}{4}$ + $\frac{1}{6}$ + …. + $\frac{1}{20}$ ) = ( 1 + $\frac{1}{2}$ + $\frac{1}{3}$ + $\frac{1}{4}$ + $\frac{1}{5}$ + $\frac{1}{6}$ + … + $\frac{1}{19}$ + $\frac{1}{20}$ ) – (1+$\frac{1}{2}$ + $\frac{1}{3}$ +…+$\frac{1}{10}$ ) = $\frac{1}{11}$ + … + $\frac{1}{20}$ ⇒ P = ( $\frac{1}{11}$ + … + $\frac{1}{20}$ ) : ( $\frac{1}{11}$ +$\frac{1}{12}$ +…+ $\frac{1}{20}$ ) ⇒ P = 1 Học Tốt =))) Bình luận
Đáp án:
Ta sẽ phân tích :
1/1.2 + 1/3.4 + 1/5.6 + …. + 1/19.20
= 1 – 1/2 + 1/3 – 1/4 + 1/5 – 1/6 + …. + 1/19 – 1/20
= ( 1 + 1/3 + 1/5 + … + 1/19) – ( 1/2 + 1/4 + 1/6 + …. + 1/20)
= ( 1 + 1/2 + 1/3 + 1/4 + 1/5 + 1/6 + … + 1/19 + 1/20) – 2.( 1/2 + 1/4 + 1/6 + …. + 1/20)
= ( 1 + 1/2 + 1/3 + 1/4 + 1/5 + 1/6 + … + 1/19 + 1/20 ) – (1+1/2+1/3+…+1/10)
= 1/11 + … + 1/20
=> P = ( 1/11 + … + 1/20) : ( 1/11+1/12+…+1/20)
=> P = 1
Giải thích các bước giải:
$\frac{1}{2}$.2 + $\frac{1}{3}$ .4 + $\frac{1}{5}$ .6 + …. + $\frac{1}{19}$.20
= 1 – $\frac{1}{2}$ +$\frac{1}{3}$ – $\frac{1}{4}$ + $\frac{1}{5}$ – $\frac{1}{6}$ + …. + $\frac{1}{19}$ – $\frac{1}{20}$
= ( 1 + $\frac{1}{3}$ + $\frac{1}{5}$ + … + $\frac{1}{19}$ ) – ( $\frac{1}{2}$ + $\frac{1}{4}$ + $\frac{1}{6}$ + …. + $\frac{1}{20}$ )
= ( 1 + $\frac{1}{2}$ + $\frac{1}{3}$ + $\frac{1}{4}$ + $\frac{1}{5}$ + $\frac{1}{6}$ … + $\frac{1}{19}$ + $\frac{1}{20}$ ) – 2.( $\frac{1}{2}$ + $\frac{1}{4}$ + $\frac{1}{6}$ + …. + $\frac{1}{20}$ )
= ( 1 + $\frac{1}{2}$ + $\frac{1}{3}$ + $\frac{1}{4}$ + $\frac{1}{5}$ + $\frac{1}{6}$ + … + $\frac{1}{19}$ + $\frac{1}{20}$ ) – (1+$\frac{1}{2}$ + $\frac{1}{3}$ +…+$\frac{1}{10}$ )
= $\frac{1}{11}$ + … + $\frac{1}{20}$
⇒ P = ( $\frac{1}{11}$ + … + $\frac{1}{20}$ ) : ( $\frac{1}{11}$ +$\frac{1}{12}$ +…+ $\frac{1}{20}$ )
⇒ P = 1
Học Tốt =)))