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Đặt A là tên của biểu thức trên
2A = \(\frac{7.2}{5.9}+\frac{7.2}{9.11}+\frac{7.2}{11.13}+\frac{7.2}{13.15}+...+\frac{7.2}{2015.2017}\)
2A = \(7\left(\frac{2}{5.9}+\frac{2}{9.11}+\frac{2}{11.13}+\frac{2}{13.15}+...+\frac{2}{2015.2017}\right)\)
2A = \(7\left(\frac{1}{5}-\frac{1}{9}+\frac{1}{9}-\frac{1}{11}+\frac{1}{11}-\frac{1}{13}+\frac{1}{13}-\frac{1}{15}+...+\frac{1}{2015}-\frac{1}{2017}\right)\)
2A = \(7\left(\frac{1}{5}-\frac{1}{2017}\right)\)
2A = \(7\cdot\frac{2012}{10085}\)
2A = \(\frac{14084}{10085}\)
A = \(\frac{14084}{10085}:2\)
A = \(\frac{7042}{10085}\)
\(\frac{7}{5.9}+\frac{7}{9.11}+\frac{7}{11.13}+\frac{7}{11.13}+...+\frac{7}{2015.2017}\)
\(=\frac{7}{5.9}+\frac{7}{2}.\left(\frac{2}{9.11}+\frac{2}{11.13}+\frac{2}{13.15}+...+\frac{2}{2015.2017}\right)\)
\(=\frac{7}{45}+\frac{7}{2}.\left(\frac{1}{9}-\frac{1}{11}+\frac{1}{11}-\frac{1}{13}+\frac{1}{13}-\frac{1}{15}+...+\frac{1}{2015}-\frac{1}{2017}\right)\)
A,x thuộc{-3,-2,-1,0,1,2,3,4}
B,x thuộc{-7,-6,-5,-4,-3,-2,-1,0,1,2,3,4,5,6}
câu c mk chịu
a) x + \(\frac{1}{6}\)=\(-\frac{3}{8}\)
x=\(\frac{-3}{8}-\frac{1}{6}\)
x=\(\frac{-13}{24}\)
b)\(\frac{1}{2}\)x + \(\frac{1}{8}\)x = \(\frac{3}{4}\)
\(\left(\frac{1}{2}+\frac{1}{8}\right)\)x = \(\frac{3}{4}\)
\(\frac{5}{8}\)x = \(\frac{3}{4}\)
x = \(\frac{3}{4}:\frac{5}{8}\)
x =\(\frac{6}{5}\)
c) 2 - l3/4-xl=7/12
l3/4-xl=17/12
nếu 3/4 - x > 0
thì 3/4 - x = 17/12
x= -2/3
nếu 3/4 - x <0
thì 3/4 - x = -17/12
x = 13/6
d) \(\left(2x-4.5\right):\frac{3}{4}-\frac{1}{3}=1\)
\(\left(2x-4.5\right):\frac{3}{4}=\frac{4}{3}\)
\(2x-4.5=1\)
2x = 5.5
x = 2.75
a, x + 1/6 = -3/8
x = -3/8 - 1/6
x = -13/24
b, 1/2x + 1/8x = 3/4
x * (1/2+1/8) = 3/4
x * 5/8 = 3/4
x = 3/4 : 5/8
x = 6/5
c, 2 - |3/4-x| = 7/12
|3/4-x| = 2 - 7/12
|3/4-x| = 17/12
=> 3/4 - x = 17/12 hoặc -17/12
# 3/4 - x = 17/12
=> x = -2/3
# 3/4 - x = -17/12
=> x = 13/6
=> x = { -2/3 ; 13/6}
d, (2x - 4,5) : 3/4 -1/3 = 1
(2x - 4,5) : 3/4 = 1 + 1/3
(2x - 4,5 ) : 3/4 = 4/3
2x - 4,5 = 4/3 * 3/4
2x - 4,5 = 1
2x = 1 + 4,5
2x = 5,5
x = 5,5 : 2
x = 2,75
\(\frac{2}{3}+\frac{8}{35}< \frac{x}{105}< \frac{1}{7}+\frac{2}{5}+\frac{1}{3}\)
\(\frac{94}{105}< \frac{x}{105}< \frac{92}{105}\)
\(\Rightarrow94< x< 92\)
mà x là số tựu nhiên => \(x\in\varnothing\)
\(\Leftrightarrow\frac{-2}{17}\le\frac{x}{17}\le\frac{2}{17}\Rightarrow x\in\left(-2;-1;0;1;2\right)\)
\(\Leftrightarrow\frac{-1}{24}\le\frac{x}{24}\le\frac{5}{24}\Rightarrow x\in\left(-1;0;1;2;3;4;5\right)\)
2 câu sau tự làm nha
\(-\frac{5}{17}+\frac{3}{17}\le\frac{x}{17}\le\frac{13}{17}+-\frac{11}{17}\)
\(\frac{-2}{17}\le\frac{x}{17}\le\frac{2}{17}\)
=> \(x\in\left\{-2;-1;0;1;2\right\}\)
\(\frac{x-7}{3}=\frac{-27}{7-x}\)
\(\Leftrightarrow\left(x-7\right)\left(7-x\right)=\left(-27\right).3\)
\(\Leftrightarrow7x-x^2-49+7x=-81\)
\(\Leftrightarrow-x^2+14x-49=-81\)
\(\Leftrightarrow-x^2+14x+32=0\)
\(\Leftrightarrow x^2-14x-32=0\)
\(\Leftrightarrow x^2+2x-16x-32=0\)
\(\Leftrightarrow x\left(x+2\right)-16\left(x+2\right)=0\)
\(\Leftrightarrow\left(x+2\right)\left(x-16\right)=0\)
\(\Leftrightarrow\orbr{\begin{cases}x+2=0\\x-16=0\end{cases}\Leftrightarrow\orbr{\begin{cases}x=-2\\x=16\end{cases}}}\)
x= 16 nhé