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a: =7/8:(2/9-18+1/36)-5/12
=-7/142-5/12=-397/852
b: =3/7(4/9+5/9:6/12)=2/3
c: =5^8(16/31-47/31)+1/3=-5^8+1/3
d: =7/2(3/8+5/8:4/15)=609/64
A) 7/38 x 9/11 +7/38 x 4/11 -7/38 x 2/11
=7/38.(9/11+4/11-2/11)
=7/38
B) 5/31 x 21/25 + 5/31 x -7/10 - 5/31 x 9/20
=5/31.(21/25-7/10-9/20)
=5/31.(-31/100)
=-1/20
1) \(A=\frac{7}{10\times11}+\frac{7}{11\times12}+\frac{7}{12\times13}+...+\frac{7}{69\times70}\)
\(A=7\times\left(\frac{1}{10\times11}+\frac{1}{11\times12}+\frac{1}{12\times13}+...+\frac{1}{69\times70}\right)\)
\(A=7\times\left(\frac{1}{10}-\frac{1}{11}+\frac{1}{11}-\frac{1}{12}+\frac{1}{12}-\frac{1}{13}+...+\frac{1}{69}-\frac{1}{70}\right)\)
\(A=7\times\left(\frac{1}{10}-\frac{1}{70}\right)\)
\(A=7\times\frac{3}{35}\)
\(A=\frac{3}{5}\)
2) \(B=\frac{1}{25\times27}+\frac{1}{27\times29}+\frac{1}{29\times31}+...+\frac{1}{73\times75}\)
\(B=\frac{1}{2}\times\left(\frac{2}{25\times27}+\frac{2}{27\times29}+\frac{2}{29\times31}+...+\frac{2}{73\times75}\right)\).
\(B=\frac{1}{2}\times\left(\frac{1}{25}-\frac{1}{27}+\frac{1}{27}-\frac{1}{29}+\frac{1}{29}-\frac{1}{31}+...+\frac{1}{73}-\frac{1}{75}\right)\)
\(B=\frac{1}{2}\times\left(\frac{1}{25}-\frac{1}{75}\right)\)
\(B=\frac{1}{2}\times\frac{2}{75}\)
\(B=\frac{1}{75}\)
3) \(C=\frac{4}{2\times4}+\frac{4}{4\times6}+\frac{4}{6\times8}+...+\frac{4}{2008\times2010}\)
\(C=\frac{4}{2}\times\left(\frac{2}{2\times4}+\frac{2}{4\times6}+\frac{2}{6\times8}+...+\frac{2}{2008\times2010}\right)\)
\(C=2\times\left(\frac{1}{2}-\frac{1}{4}+\frac{1}{4}-\frac{1}{6}+\frac{1}{6}-\frac{1}{8}+...+\frac{1}{2008}-\frac{1}{2010}\right)\)
\(C=2\times\left(\frac{1}{2}-\frac{1}{2010}\right)\)
\(C=2\times\frac{502}{1005}\)
\(C=\frac{1004}{1005}\)
_Chúc bạn học tốt_
x + 27 + 7.x = 187
x + 7x + 27 = 187
8x = 187 - 27
8x = 160
x = 160 : 8
x = 20
Vậy x = 20
x + 27 +7 + x = 187
2x + 27 + 7 = 187
2x + 34 = 187
2x = 187 - 34
2x = 153
x = 153/2
Câu 1:
\(=\dfrac{21}{31}+\dfrac{1}{3}-\dfrac{44}{53}+\dfrac{10}{31}-\dfrac{9}{53}=\dfrac{1}{3}\)
Câu 2:
1: =>1,3x=-1,31
=>130x=-131
=>x=-131/130
2: =>(4,5-2x)=11/14:(-11/7)=-7/14=-1/2=-0,5
=>2x=5
=>x=5/2
Bài 1 : Bài giải
\(-2\left(-3-4x\right)-3\left(3x-7\right)=31\)
\(6+8x-9x-21=31\)
\(-x-15=31\)
\(-x=31+15\)
\(-x=46\)
\(x=-46\)
b, \(10\left(x-7\right)=8\left(x-4\right)+x\)
\(10x-70=8x-32+x\)
\(10x-70=9x-32\)
\(10x-9x=-32+70\)
\(x=38\)
c, \(2\left|x-1\right|=3\cdot\left(5-1\right)\)
\(2\left|x-1\right|=15-3\)
\(2\left|x-1\right|=12\)
\(\left|x-1\right|=12\text{ : }2\)
\(\left|x-1\right|=6\)
\(\Rightarrow\orbr{\begin{cases}x-1=-6\\x-1=6\end{cases}}\Rightarrow\orbr{\begin{cases}x=-5\\x=7\end{cases}}\)
\(\Rightarrow\text{ }x\in\left\{-5\text{ ; }7\right\}\)
d, \(2\left(x+3\right)-2\left(x-3\right)=x\)
\(2\left(x+3-x-3\right)=x\)
\(2\cdot0=x\)
\(x=0\)
e, \(\left(x+3\right)\left(x-4\right)=0\)
\(\Rightarrow\orbr{\begin{cases}x+3=0\\x-4=0\end{cases}}\Rightarrow\orbr{\begin{cases}x=-3\\x=4\end{cases}}\)
\(\Rightarrow\text{ }x\in\left\{-3\text{ ; }4\right\}\)
a, \(-2\left(-3-4x\right)-3\left(3x-7\right)=31\)
\(6+8x-9x-21=31\)
\(-x-15=31\)
\(-x=31+15\)
\(-x=46\)
\(x=-46\)
b, \(10\left(x-7\right)=8\left(x-4\right)+x\)
\(10x-70=8x-32+x\)
\(10x-70=9x-32\)
\(10x-9x=-32+70\)
\(x=38\)
c, \(2\left|x-1\right|=3\cdot\left(5-1\right)\)
\(2\left|x-1\right|=15-3\)
\(2\left|x-1\right|=12\)
\(\left|x-1\right|=12\text{ : }2\)
\(\left|x-1\right|=6\)
\(\Rightarrow\orbr{\begin{cases}x-1=-6\\x-1=6\end{cases}}\Rightarrow\orbr{\begin{cases}x=-5\\x=7\end{cases}}\)
\(\Rightarrow\text{ }x\in\left\{-5\text{ ; }7\right\}\)
d, \(2\left(x+3\right)-2\left(x-3\right)=x\)
\(2\left(x+3-x-3\right)=x\)
\(2\cdot0=x\)
\(x=0\)
e, \(\left(x+3\right)\left(x-4\right)=0\)
\(\Rightarrow\orbr{\begin{cases}x+3=0\\x-4=0\end{cases}}\Rightarrow\orbr{\begin{cases}x=-3\\x=4\end{cases}}\)
\(\Rightarrow\text{ }x\in\left\{-3\text{ ; }4\right\}\)
(x+1)+(x+4)+(x+7)+.....+(x+31)=187
(x+x+x+...+x)+(1+4+7+....+31)=187
11x+11.32:2=187
11.(x+16)=187
x+16=17
x=11
vậy x=11
( x + 1 ) + ( x + 4 ) + ( x + 7 ) + ... + ( x + 31 ) = 187
x + 1 + x + 4 + x + 7 + ... + x + 31 = 187
( x + x + x + ... + x ) + ( 1 + 4 + 7 + ... + 31 ) = 187
Đặt x + x + x + ... + x = A; 1 + 4 + 7 + ... + 31 = B
Dãy B có số số hạng là:
( 31 - 1 ) : 3 + 1 = 11 ( số hạng )
=> A = 11x
Tổng của dãy B là:
( 31 + 1 ) . 11 : 2 = 176
Ta có:
A + B = 187
=> 11x + 176 = 187
=> 11x = 187 - 176
=> 11x = 11
=> x = 1