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LV
3
18 tháng 7 2023
`@` `\text {Ans}`
`\downarrow`
\(1793\cdot\left(x\div1792\right)=0\)
`\Rightarrow x \div 1792 = 0 \div 1793`
`\Rightarrow x \div 1792 = 0`
`\Rightarrow x = 0. 1792`
`\Rightarrow x = 0`
Vậy, `x = 0.`
VN
Võ Ngọc Phương
CTVHS
VIP
18 tháng 7 2023
\(1793.\left(x:1792\right)=0\)
\(=>x:1792=0:1793\)
\(=>x:1792=0\)
\(=>x=0.1792\)
\(=>x=0\)
NT
2
10 tháng 5 2019
\(A=\frac{4}{2.5}+\frac{4}{5.8}+\frac{4}{8.11}+...+\frac{4}{65.68}\)
\(A=\frac{4}{3}.\left(\frac{3}{2.5}+\frac{3}{5.8}+\frac{3}{8.11}+...+\frac{3}{65.68}\right)\)
\(A=\frac{4}{3}.\left(\frac{1}{2}-\frac{1}{5}+\frac{1}{5}-\frac{1}{8}+...+\frac{1}{65}-\frac{1}{68}\right)\)
\(A=\frac{4}{3}.\left[\frac{1}{2}+\left(\frac{1}{5}-\frac{1}{5}\right)+\left(\frac{1}{8}-\frac{1}{8}\right)+...+\left(\frac{1}{65}-\frac{1}{65}\right)-\frac{1}{68}\right]\)
\(A=\frac{4}{3}.\left[\frac{1}{2}-\frac{1}{68}\right]\)
\(A=\frac{4}{3}.\frac{33}{68}\)
\(A=\frac{11}{17}\)
~ Hok tốt ~
TN
10 tháng 5 2019
\(A=\frac{4}{3}\left(\frac{1}{2}-\frac{1}{5}+\frac{1}{5}-\frac{1}{8}+....+\frac{1}{65}-\frac{1}{68}\right)\)
\(=\frac{4}{3}\left(\frac{1}{2}-\frac{1}{68}\right)\)
\(=\frac{4}{3}\times\frac{33}{68}=\frac{11}{17}\)
NN
Nguyễn Ngọc Anh Minh
CTVHS
VIP
19 tháng 7 2023
a/
\(A=1.2+1.2+2.3+2.2+3.4+3.2+...+66.67+66.2=\)
\(=\left(1.2+2.3+3.4+...+66.67\right)+2\left(1+2+3+...+66\right)\)
Đặt
\(B=1+2+3+...+66=\dfrac{66\left(1+66\right)}{2}=2211\)
Đặt
\(C=1.2+2.3+3.4+...+66.67\)
\(3C=1.2.3+2.3.3+3.4.3+...+66.67.3=\)
\(=1.2.3+2.3.\left(4-1\right)+3.4.\left(5-2\right)+...+66.67.\left(68-65\right)=\)
\(=1.2.3-1.2.3+2.3.4-2.3.4+3.4.5-...-65.66.67+66.67.68=\)
\(=66.67.68\Rightarrow C=\dfrac{66.67.68}{3}=22.67.68\)
\(\Rightarrow A=C+2B\) Bạn tự tính nhé
b/
\(B=2\left(1.50+2.49+3.48+...+25.26\right)=\)
Ta có
\(C=1.50+2.49+3.48+...+25.26=\)
\(\left(50-49\right).50+\left(50-48\right).49+\left(50-47\right).48+...+\left(50-25\right).26=\)
\(=50.50-49.50+50.49-48.49+50.48-47.48+50.26-25.26=\)
\(=50.\left(26+27+28+...+50\right)-\left(25.26+26.27+27.28+...+49.50\right)\)
Ta có
\(D=26+27+28+...+50=\dfrac{25.\left(26+50\right)}{2}=950\)
Ta có
\(E=25.26+26.27+27.28+...+49.50\)
\(3E=25.26.3+26.27.3+27.28.3+...+49.50.3=\)
\(=25.26.\left(27-24\right)+26.27.\left(28-25\right)+...+49.50.\left(51-48\right)=\)
\(=-24.25.26+25.26.27-25.26.27+26.27.28-...-48.49.50+49.50.51=\)
\(=49.50.51-24.25.26\)
\(\Rightarrow E=\dfrac{49.50.51-24.25.26}{3}\)
\(\Rightarrow C=50D-E\)
\(B=2C\)
Bạn tự tính nhé
16 tháng 5 2016
S = 1/3 . (1/2 - 1/5 + 1/5 - 1/8 + ... + 1/17 - 1/20)
= 1/3 . (1/2 - 1/20)
= 1/3 . 9/20
= 3/20
NN
Nguyễn Ngọc Anh Minh
CTVHS
VIP
16 tháng 5 2016
\(3S=\frac{5-2}{2.5}+\frac{8-5}{5.8}+\frac{11-8}{8.11}+...+\frac{20-17}{17.20}\)
\(3S=\frac{1}{2}-\frac{1}{5}+\frac{1}{5}-\frac{1}{8}+\frac{1}{8}-\frac{1}{11}+...+\frac{1}{17}-\frac{1}{20}=\frac{1}{2}-\frac{1}{20}=\frac{9}{20}\)
\(S=\frac{9}{20}:3=\frac{3}{20}\)
24 tháng 7 2019
\(\frac{1}{2.5}+\frac{1}{5.8}+...+\frac{1}{\left(3n-1\right)\left(3n+2\right)}\)
\(=\frac{1}{3}.\left(\frac{3}{2.5}+\frac{3}{5.8}+...+\frac{3}{\left(3n-1\right)\left(3n+2\right)}\right)\)
\(=\frac{1}{3}.\left(\frac{1}{2}-\frac{1}{5}+\frac{1}{5}-\frac{1}{8}+...+\frac{1}{3n-1}-\frac{1}{3n+2}\right)\)
\(=\frac{1}{3}.\left(\frac{1}{2}-\frac{1}{3n+2}\right)\)
\(=\frac{1}{3}.\frac{3n}{2.\left(3n+2\right)}\)
\(=\frac{n}{2\left(3n+2\right)}\)
TT
0
NM
3
15 tháng 4 2021
Đặt A = \(\frac{1}{2.5}+\frac{1}{5.8}+...+\frac{1}{23.26}+\frac{1}{26.29}\)
3A = \(\frac{3}{2.5}+\frac{3}{5.8}+...+\frac{3}{23.26}+\frac{3}{26.29}\)
= \(\frac{1}{2}-\frac{1}{5}+\frac{1}{5}-\frac{1}{8}+...+\frac{1}{23}-\frac{1}{26}+\frac{1}{26}-\frac{1}{29}\)
= \(\frac{1}{2}-\frac{1}{29}\)\(=\frac{27}{58}\)
A = \(\frac{27}{58}:3=\frac{9}{58}\)
XO
15 tháng 4 2021
\(\frac{1}{2.5}+\frac{1}{5.8}+...+\frac{1}{23.26}+\frac{1}{26.29}=\frac{1}{3}.\left(\frac{3}{2.5}+\frac{3}{5.8}+...+\frac{3}{23.26}+\frac{3}{26.29}\right)\)
\(=\frac{1}{3}.\left(\frac{1}{2}-\frac{1}{5}+\frac{1}{5}-\frac{1}{8}+...+\frac{1}{23}-\frac{1}{26}+\frac{1}{26}-\frac{1}{29}\right)=\frac{1}{3}\left(\frac{1}{2}-\frac{1}{29}\right)\)
\(=\frac{1}{3}.\frac{27}{58}=\frac{9}{58}\)
NT
2
AD
29 tháng 10 2023
( 19x + 2.52 ) : 14 = ( 13 - 8 )2- 4 2
( 19x + 2.52 ) : 14 = 52- 4 2
( 19x + 2.52 ) : 14 = 25- 16
( 19x + 2.52 ) : 14 =9
( 19x + 50 ) : 14 =9
19x + 50=9 . 14
19x + 50=126
19x=126-50
19x=76
x=76:19
x=4
KV
29 tháng 10 2023
(19x + 2.5²) : 14 = (13 - 8)² - 4²
(19x + 2.25) : 14 = 5² - 16
(19x + 50) : 14 = 25 - 16
(19x + 50) : 14 = 9
19x + 50 = 9 . 14
19x + 50 = 126
19x = 126 - 50
19x = 76
x = 76 : 19
x = 4
=2.25.7.9/10.15.21
rut gon:
=9/9
=1
\(\frac{2.5^2.7.9}{10.15.21}\)
\(=\frac{2.5.5.7.3.3}{2.5.5.3.7.3}\)
\(=\frac{1}{1}\)
\(=1\)
Chúc bạn học tốt!!!