61721

Lời giải

720: a x ( 3 + 5 ) = 6 

=> a x 8 = 720 : 6 
=> a x 8 = 120 
=> a = 120 : 8 
=> a = 15 

\(a.5+a=360:6\)

\(a\left(5+1\right)=60\)

\(a.6=60\)

\(a=\frac{60}{6}\)

Vậy\(a=10\)

a x 5 +a = 360 / 6

a (5+1) = 60

a x 6 = 60

a = 10

vậy a = 10

 hc tốt

\(720:\left(a.2+3\right)=2.3\)

\(a.2+3=720:6\)

\(a.2+3=120\)

\(a.2=120-3\)

\(a.2=117\)

Vậy \(a=\frac{117}{2}\)

(2x - 4)³ = 8

(2x - 4)³ = 2³

2x - 4 = 2

2x = 2 + 4

2x = 6

x = 6 : 2

x = 3

\(\frac{720}{41-\left(2x-5\right)}=2^3\times5\)

\(\frac{720}{41-2x+5}=8\times5\)

\(46-2x=\frac{720}{40}\)

\(2x=46-18\)

2x = 28

x = 28 : 2

x = 14

\(\left(x+1\right)+\left(x+2\right)+\left(x+3\right)+...+\left(x+100\right)=5750\)

\(\left(x+x+x+...+x\right)+\left(1+2+3+...+100\right)=5750\)

\(\Rightarrow100x+5050=5750\Rightarrow x=5750-5050\)

\(100x=700\Rightarrow x=700:100=7\)

\(a,\text{ }720\text{ : }\left[41-\left(2x-5\right)\right]=2^3\cdot5\)

\(720\text{ : }\left[42-2x+5\right]=8\cdot5\)

\(720\text{ : }\left[42+5-2x\right]=40\)

\(720\text{ : }\left[47-2x\right]=40\)

\(47-2x=720\text{ : }40\)

\(47-2x=18\)

\(2x=47-18\)

\(2x=29\)

\(x=\frac{29}{2}\)

\(b,\text{ }\left(x+1\right)+\left(x+2\right)+\left(x+3\right)+...+\left(x+100\right)=5750\)

\(\left(x+x+x+...+x\right)+\left(1+2+3+...+100\right)=5750\)

\(100x+\left[\left(100-1\right)\text{ : }1+1\right]\text{ x }\left(100+1\right)\text{ }:\text{ }2=5750\)

\(100x+100\text{ x }101\text{ : }2=5750\)

\(100x+10100\text{ : }2=5750\)

\(100x+5050=5750\)

\(100x=5750-5050\)

\(100x=700\)

\(x=700\text{ : }100\)

\(x=7\)

\(\frac{3}{a+b\sqrt{3}}-\frac{2}{a-b\sqrt{3}}=720\sqrt{3}\)

<=> \(a-5b\sqrt{3}=720\sqrt{3}\left(a^2-3b^2\right)\)

<=> \(a=\sqrt{3}\left(5b+720a^2-2160b^2\right)\)

Do a ,b là số hữu tỉ 

=> \(a=5b+720a^2-2160b^2=0\)

=> \(\hept{\begin{cases}a=0\\5b-2160b^2=0\end{cases}}\)

Mà a,b không đồng thời bằng 0

=> \(a=0;b=\frac{1}{432}\)

Vậy \(a=0;b=\frac{1}{432}\)

giúp mik với

mik cần gấp

Chỉ làm bài khó thôi nhé:::::::::::::::

\(\frac{1}{3}+\frac{1}{6}+\frac{1}{10}+...+\frac{2}{x.\left(x+1\right)}=\frac{2016}{2018}\)

\(\Rightarrow\frac{2}{6}+\frac{2}{12}+\frac{2}{20}+....+\frac{2}{x.\left(x+1\right)}=\frac{2016}{2018}\)

\(\Rightarrow2.\left(\frac{1}{6}+\frac{1}{12}+\frac{1}{20}+...+\frac{1}{x.\left(x+1\right)}\right)=\frac{2016}{2018}\)

\(\Rightarrow\frac{1}{2.3}+\frac{1}{3.4}+\frac{1}{4.5}+...+\frac{1}{x.\left(x+1\right)}=\frac{1013}{2018}\)

\(\Rightarrow\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+...+\frac{1}{x}-\frac{1}{x+1}=\frac{1013}{2018}\)

\(\Rightarrow\frac{1}{2}-\frac{1}{x+1}=\frac{1013}{2018}\)

\(\Rightarrow\frac{1}{x+1}=\frac{1}{2018}\Rightarrow x+1=2018\Rightarrow x=2017\)