A )1/8+1/24+1/48+1/80+1/120 Tính ra từng bước. b) tìm x biết 1200 :24 -(19 -x ) =38 tính ra từng bước hết nhá
c) 2-[(5 5/24 +x) -7 5/24 ]= 0
Tính ra từng bước tớ cần gấp vào tối nay
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\(\left\{{}\begin{matrix}\left\{{}\begin{matrix}3x-15=45\Leftrightarrow3x=60\Leftrightarrow x=20\\35-5x=50\Leftrightarrow5x=-15\Leftrightarrow x=-3\end{matrix}\right.\\\left\{{}\begin{matrix}\left(2x-5\right)+17=6\Leftrightarrow2x+5=-11\Leftrightarrow2x=-16\Leftrightarrow x=-8\\10-2\left(4-3x\right)=-4\Leftrightarrow8-6x=14\Leftrightarrow6x=-6\Leftrightarrow x=-1\end{matrix}\right.\\\left\{{}\begin{matrix}-12+3\left(-x+7\right)=-18\Leftrightarrow-3x+21=-6\Leftrightarrow-3x=-27\Leftrightarrow x=9\\24:\left(3x-2\right)=-3\Leftrightarrow3x-2=-8\Leftrightarrow3x=-6\Leftrightarrow x=-2\end{matrix}\right.\\-45:5\left(-3-2x\right)=3\Leftrightarrow-15-10x=-15\Leftrightarrow10x=0\Leftrightarrow x=0\end{matrix}\right.\)
a) ( 72 - 8 x 9 ) : ( 20 + 21 + 22 + 23 + 24 + 25 )
= ( 72 - 72 ) : ( 20 + 21 + 22 + 23 + 24 + 25 )
= 0 : ( 20 + 21 + 22 + 23 + 24 + 25 )
= 0
b) ( 500 x 9 - 250 x 18 ) x ( 1 + 2 + 3 + ... + 9 )
= ( 500 x 9 - 250 x 2 x 9 ) x ( 1 + 2 + 3 + ... + 9 )
= ( 500 x 9 - 500 x 9 ) x ( 1 + 2 + 3 + ... + 9 )
= 0 x ( 1 + 2 + 3 + ... + 9 )
= 0
1200-31/40=47969/40
câu 2 =45/56+25/56=(45+25)/56=70/56=5/4
c) \(\dfrac{11}{10}-\dfrac{-7}{24}=\dfrac{11}{10}+\dfrac{7}{24}=\dfrac{167}{120}\)
e) \(\dfrac{-8}{3}\cdot\dfrac{15}{7}=\dfrac{-120}{21}=\dfrac{-40}{7}\)
f) \(\dfrac{-2}{5}\cdot4\dfrac{1}{2}=\dfrac{-2}{5}\cdot\dfrac{9}{2}=-\dfrac{9}{5}\)
g) \(\dfrac{5}{3}:\dfrac{5}{-3}=\dfrac{5}{3}:\dfrac{-5}{3}=\dfrac{5}{3}\cdot\dfrac{-3}{5}=-1\)
h) \(\dfrac{5}{4}:\left(-9\right)=\dfrac{5}{4}:\dfrac{-9}{1}=\dfrac{5}{4}\cdot\dfrac{-1}{9}=-\dfrac{5}{36}\)
Bài 2:
1: \(\dfrac{x}{12}-\dfrac{5}{6}=\dfrac{1}{12}\)
=>\(\dfrac{x}{12}=\dfrac{1}{12}+\dfrac{5}{6}=\dfrac{1}{12}+\dfrac{10}{12}=\dfrac{11}{12}\)
=>x=11
2: \(\dfrac{2}{3}-1\dfrac{4}{15}x=-\dfrac{3}{5}\)
=>\(\dfrac{2}{3}-\dfrac{19}{15}x=-\dfrac{3}{5}\)
=>\(\dfrac{19}{15}x=\dfrac{2}{3}+\dfrac{3}{5}=\dfrac{10+9}{15}=\dfrac{19}{15}\)
=>\(x=\dfrac{19}{15}:\dfrac{19}{15}=1\)
3: \(\dfrac{\left(-3\right)^x}{81}=-27\)
=>\(\left(-3\right)^x=\left(-3\right)^3\cdot\left(-3\right)^4=\left(-3\right)^7\)
=>x=7
4: \(\left|x+0,237\right|=0\)
=>x+0,237=0
=>x=-0,237
5: \(\left(x-1\right)^2=25\)
=>\(\left[{}\begin{matrix}x-1=5\\x-1=-5\end{matrix}\right.\)
=>\(\left[{}\begin{matrix}x=6\\x=-4\end{matrix}\right.\)
6: \(\left|2x-1\right|=5\)
=>\(\left[{}\begin{matrix}2x-1=5\\2x-1=-5\end{matrix}\right.\)
=>\(\left[{}\begin{matrix}2x=6\\2x=-4\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x=3\\x=-2\end{matrix}\right.\)
7: \(\left(x-1\right)^3=-\dfrac{8}{27}\)
=>\(\left(x-1\right)^3=\left(-\dfrac{2}{3}\right)^3\)
=>\(x-1=-\dfrac{2}{3}\)
=>\(x=-\dfrac{2}{3}+1=\dfrac{1}{3}\)
8: \(1\dfrac{2}{3}:\dfrac{x}{4}=6:0,3\)
=>\(\dfrac{5}{3}:\dfrac{x}{4}=20\)
=>\(\dfrac{20}{3x}=20\)
=>3x=20/20=1
=>\(x=\dfrac{1}{3}\)
9: \(2\dfrac{2}{3}:x=1\dfrac{7}{9}:2\dfrac{2}{3}\)
=>\(\dfrac{\dfrac{8}{3}}{x}=\dfrac{\dfrac{16}{9}}{\dfrac{8}{3}}\)
=>\(\dfrac{16}{9}\cdot x=\dfrac{8}{3}\cdot\dfrac{8}{3}=\dfrac{64}{9}\)
=>16x=64
=>x=64/16=4
Bài 3:
1: Ta có: x-24=y
=>x-y=24
mà \(\dfrac{x}{7}=\dfrac{y}{3}\)
nên Áp dụng tính chất của dãy tỉ số bằng nhau, ta được:
\(\dfrac{x}{7}=\dfrac{y}{3}=\dfrac{x-y}{7-3}=\dfrac{24}{4}=6\)
=>\(x=6\cdot7=42;y=6\cdot3=18\)
2: \(\dfrac{x}{5}=\dfrac{y}{7}=\dfrac{z}{2}\)
mà x-y=48
nên Áp dụng tính chất của dãy tỉ số bằng nhau, ta được:
\(\dfrac{x}{5}=\dfrac{y}{7}=\dfrac{z}{2}=\dfrac{x-y}{5-7}=\dfrac{48}{-2}=-24\)
=>\(x=-24\cdot5=-120;y=-24\cdot7=-168;z=-24\cdot2=-48\)
3: \(\dfrac{x-1}{2005}=\dfrac{3-y}{2006}\)
mà x-y=4009
nên Áp dụng tính chất của dãy tỉ số bằng nhau, ta được:
\(\dfrac{x-1}{2005}=\dfrac{3-y}{2006}=\dfrac{x-1+3-y}{2005+2006}=\dfrac{4009+2}{4011}=1\)
=>\(x-1=2005;3-y=2006\)
=>x=2005+1=2006; y=3-2006=-2003
5: \(\dfrac{x}{3}=\dfrac{y}{5}=\dfrac{z}{7}\)
mà 2x+3y-z=-14
nên Áp dụng tính chất của dãy tỉ số bằng nhau, ta được:
\(\dfrac{x}{3}=\dfrac{y}{5}=\dfrac{z}{7}=\dfrac{2x+3y-z}{2\cdot3+3\cdot5-7}=\dfrac{-14}{14}=-1\)
=>\(x=-3;y=-5;z=-7\)
Bạn tách ra từng CH khác nhau đi nhé. Gộp 1 trong tất cả rất khó nhìn và lâu.
b) X x 3,7 + X x 6,3 = 120 |
X x ( 3,7 + 6,3 ) = 120
X x 10 = 120
X = 120 : 10
X = 12
Vậy X = 12
a) 2/3x +1/2 = 1/10
=> 2/3x = 1/10 - 1/2
2/3x = -2/5
=> x = -2/5 : 2/3
x = -3/5
b) (4,5 - 2x) : 3/4 = \(1\frac{1}{3}=\frac{4}{3}\)
=> 4,5 - 2x = 4/3 x 3/4
4,5 - 2x = 1
-2x = 4,5 - 1
-2x = 3,5
=> x = 3,5 : (-2)
x = - 1,75
c) x/4 = 5/20
=> x = 5/20 x 4
x = 1
d) ?????
2/3x+1/2=1/10
<=>2/3x=1/10-1/2
<=>2/3x=-2/10
=>x=-2/10 chia 2/3=-3/10
ý kia tương tự
\(\frac{1}{8}+\frac{1}{24}+\frac{1}{48}+\frac{1}{80}+\frac{1}{120}\)
\(=\frac{1}{2}(\frac{1}{2.4}+\frac{1}{4.6}+\frac{1}{6.8}+\frac{1}{8.10}+\frac{1}{10.12})\)
\(=\frac{1}{2}(\frac{1}{2}-\frac{1}{4}+\frac{1}{4}-\frac{1}{6}+..+\frac{1}{10}-\frac{1}{12})\)
\(=\frac{1}{2}\cdot\left(\frac{1}{2}-\frac{1}{12}\right)=\frac{1}{2}\cdot\frac{5}{12}=\frac{5}{24}\)
\(1200:24-\left(19-x\right)=38\)
\(\Leftrightarrow50-\left(19-x\right)=38\)
\(\Leftrightarrow19-x=50-38\)
\(\Leftrightarrow19-x=12\)
\(\Leftrightarrow x=7\)