tim x biet :x+5-7+1+5+8-9-1+2+4+5.4-4<98
giai cach lam ra nha
làm nhanh tớ đang cần gấp
K
Khách
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SH
0
HK
6
5 tháng 8 2017
Ta có : \(\left(2x+3\right)\left(x-7\right)=0\)
\(\Leftrightarrow\orbr{\begin{cases}2x+3=0\\x-7=0\end{cases}}\)
\(\Leftrightarrow\orbr{\begin{cases}2x=-3\\x=7\end{cases}}\)
\(\Leftrightarrow\orbr{\begin{cases}x=-\frac{3}{2}\\x=7\end{cases}}\)
16 tháng 8 2019
\(a,x-7\frac{5}{8}=1\frac{1}{4}\)
=> \(x-\frac{61}{8}=\frac{5}{4}\)
=> \(x=\frac{5}{4}+\frac{61}{8}\)
=> \(x=\frac{10}{8}+\frac{61}{8}=\frac{71}{8}=8\frac{7}{8}\)
\(b,x+7\frac{5}{8}=9\frac{1}{4}\)
=> \(x+\frac{43}{5}=\frac{37}{4}\)
=> \(x=\frac{37}{4}-\frac{43}{5}=\frac{13}{20}\)
\(c,\left[x-7\frac{5}{8}\right]:\frac{1}{2}=3\)
=> \(\left[x-\frac{61}{8}\right]=3\cdot\frac{1}{2}\)
=> \(\left[x-\frac{61}{8}\right]=\frac{3}{2}\)
=> \(x-\frac{61}{8}=\frac{3}{2}\)
=> \(x=\frac{3}{2}+\frac{61}{8}=\frac{12}{8}+\frac{61}{8}=\frac{73}{8}=9\frac{1}{8}\)
d, \(\frac{x}{1\cdot3}+\frac{x}{3\cdot5}+\frac{x}{5\cdot7}+...+\frac{x}{97\cdot99}=99\)
=> \(\frac{x}{2}\left[\frac{2}{1\cdot3}+\frac{2}{3\cdot5}+\frac{2}{5\cdot7}+...+\frac{2}{97\cdot99}\right]=99\)
=> \(\frac{x}{2}\left[1-\frac{1}{3}+\frac{1}{3}-\frac{1}{5}+...+\frac{1}{97}-\frac{1}{99}\right]=99\)
=> \(\frac{x}{2}\left[1-\frac{1}{99}\right]=99\)
=> \(\frac{x}{2}\cdot\frac{98}{99}=99\)
=> \(\frac{98x}{198}=99\)
=> 98x = 99 . 198
=> 98x = 19602
=> x = 19602 : 98 = 9801/49
16 tháng 8 2019
a) \(x-7\frac{5}{8}=1\frac{1}{4}\)
=> \(x=\frac{5}{4}+\frac{61}{8}\)
=> \(x=\frac{71}{8}\)
b) \(x+7\frac{5}{8}=9\frac{1}{4}\)
=> \(x=\frac{37}{4}-\frac{61}{8}\)
=> \(x=\frac{13}{8}\)
c) \(\left(x-7\frac{5}{8}\right):\frac{1}{2}=3\)
=> \(x-\frac{61}{8}=3.\frac{1}{2}\)
=> \(x-\frac{61}{8}=\frac{3}{2}\)
=> \(x=\frac{3}{2}+\frac{61}{8}\)
=> \(x=\frac{73}{8}\)
d) \(\frac{x}{1.3}+\frac{x}{3.5}+...+\frac{x}{97.99}=99\)
=> \(x.\frac{1}{2}.\left(\frac{2}{1.3}+\frac{2}{3.5}+...+\frac{2}{97.99}\right)=99\)
=> \(\frac{1}{2}x\left(1-\frac{1}{3}+\frac{1}{3}-\frac{1}{5}+....+\frac{1}{97}-\frac{1}{99}\right)=99\)
=> \(x\left(1-\frac{1}{99}\right)=99:\frac{1}{2}\)
=> \(x.\frac{98}{99}=198\)
=> \(x=198:\frac{98}{99}=\frac{9801}{49}\)
K
2
10 tháng 11 2016
Ta có : ( x+1 ) + ( x + 2 ) + ( x + 3 ) + ( x + 4 ) + ( x + 5 ) = 30
( x + x + x +x +x ) + ( 1 + 2 + 3 + 4 + 5 ) = 30
x * 5 + 15 = 30
x * 5 = 30 - 15
x * 5 = 15
x = 15 : 5
x = 3
Vậy x = 3
Duyệt đi , chúc bạn học giỏi
10 tháng 11 2016
(x + 1) + (x + 2) + (x + 3) + (x + 4) + (x + 5) = 4 + 5 + 6 + 7 + 8
x + 1 + x + 2 + x + 3 + x + 4 + x + 5 = 30
\(x\)x 5 + 15 = 30
\(x\)x 5 = 30 - 15 = 15
x = 15 : 5 = 3
R
8 tháng 7 2019
a)15/8+3/4-5/12
=45+18-10/24
=53/24
b)11/24.12/33+5/6
=11.12/12.2.11.3+5/6
=1/6+5/6
=6/6=1
c)15/8+7/24:5/8
=15/8+7/24.8/5
=15/8+7.8/3.8.5
=15/8+7/15
=đề sai, nếu đúng thì như này
=8/15+7/15
=15/15=1
LL
1
18 tháng 3 2017
a) \(\dfrac{x}{15}\)=\(\dfrac{x-2}{30}\)
=>30x=15 (x-2)
=>30x=15x-30
=>30x-15x=-30
=>15x =-30
=>x =-2
b)\(\dfrac{7}{8}\)<\(\dfrac{x}{80}\)<\(\dfrac{9}{10}\)
=>\(\dfrac{70}{80}\)<\(\dfrac{x}{80}\)<\(\dfrac{72}{80}\)
=> 70<x<72
=>x=71
c)\(\dfrac{1}{6}\)<\(\dfrac{5}{x}\)<\(\dfrac{1}{4}\)
=>\(\dfrac{5}{30}\)<\(\dfrac{5}{x}\)<\(\dfrac{5}{20}\)
=>20<x<30
=>x={21;22;23;24;25;26;27;28;29}
LL
3
13 tháng 4 2017
a)
\(\dfrac{2}{3}\cdot x-\dfrac{4}{7}=\dfrac{1}{8}\\ \dfrac{2}{3}\cdot x=\dfrac{1}{8}+\dfrac{4}{7}\\ \dfrac{2}{3}\cdot x=\dfrac{39}{56}\\ x=\dfrac{39}{56}:\dfrac{2}{3}\\ x=\dfrac{117}{112}\)
b)
\(\dfrac{2}{7}-\dfrac{8}{9}\cdot x=\dfrac{2}{3}\\ \dfrac{8}{9}\cdot x=\dfrac{2}{7}-\dfrac{2}{3}\\ \dfrac{8}{9}\cdot x=-\dfrac{8}{21}\\ x=-\dfrac{8}{21}:\dfrac{8}{9}\\ x=-\dfrac{3}{7}\)
c)
\(\dfrac{4}{7}+\dfrac{5}{9}:x=\dfrac{1}{5}\\ \dfrac{5}{9}:x=\dfrac{1}{5}-\dfrac{4}{7}\\ \dfrac{5}{9}:x=-\dfrac{13}{35}\\ x=\dfrac{5}{9}:\left(-\dfrac{13}{35}\right)\\ x=-\dfrac{175}{117}\)
lam nhanh nhe
x\(\in\left\{-\infty;74\right\}\)