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Bài 1:
a) −x + 8 = −17
−x = −17 − 8
−x = −25
⇒ x = 25
Vậy x = 25
b) 35 − x = 37
x = 35 − 37
x = −2
Vậy x = −2
c) x − 45 = −17
x = −17 + 45
x = 28
Vậy x = 28
d) |x + 1| = 20 (>0)
TH1: x + 1 = 20 TH2: x + 1 = −20
x = 20 − 1 x = −20 − 1
x = 19 x = −21
Vậy x∈\(\left\{-21;19\right\}\)
e) |x − 3| − 16 = −4
|x − 3| = −4 + 16
|x − 3| = 12 (>0)
TH1: x − 3 = 12 TH2: x − 3 = −12
x = 12+3 x = −12 + 3
x = 15 x = −9
Vậy x∈\(\left\{-9;15\right\}\)
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| 4 - 2x | + | 2x - 1 | = 3
Toán lớp 7, Tìm x dạng 4, bạn nào đã học thì lập bảng xét dấu giúp mik và cho mik kết quả nhé. Thanks ạ !
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a, \(\frac{22}{5}+\frac{1}{2}\cdot x^2=4\cdot\frac{8}{5}\)
=> \(\frac{22}{5}+\frac{1}{2}\cdot x^2=\frac{32}{5}\)
=> \(\frac{1}{2}\cdot x^2=\frac{32}{5}-\frac{22}{5}\)
=> \(\frac{1}{2}\cdot x^2=2\)
=> \(x^2=2:\frac{1}{2}=4\)
=> x = 2 hoặc x = -2
\(b,\frac{7}{2}-\left|x-\frac{1}{3}\right|=\frac{5}{2}\)
=> \(\left|x-\frac{1}{3}\right|=\frac{7}{2}-\frac{5}{2}\)
=> \(\left|x-\frac{1}{3}\right|=1\)
=> \(x-\frac{1}{3}=1\)hoặc \(x-\frac{1}{3}=-1\)
=> x = 1 + 1/3 hoặc x = -1 + 1/3
=> x = 4/3 hoặc x = -2/3
c, \(\left[x-\frac{1}{2}\right]\left[-3-\frac{x}{2}\right]=0\)
=> x - 1/2 = 0 hoặc -3 - x/2 = 0
=> x = 0 + 1/2 hoặc x/2 = -3
=> x = 1/2 hoặc x = -6
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a) \(2x+\frac{3}{15}=\frac{7}{5}\)
=> \(2x=\frac{7}{5}-\frac{3}{15}=\frac{21}{15}-\frac{3}{15}=\frac{18}{15}\)
=> \(x=\frac{18}{15}:2=\frac{18}{15}\cdot\frac{1}{2}=\frac{9}{15}\cdot\frac{1}{1}=\frac{9}{15}\)
b) \(x-\frac{2}{9}=\frac{8}{3}\)
=> \(x=\frac{8}{3}+\frac{2}{9}\)
=> \(x=\frac{24}{9}+\frac{2}{9}=\frac{26}{9}\)
c) \(\frac{-8}{x}=\frac{-x}{18}\)
=> x(-x) = (-8).18
=> -x2 = -144
=> x2 = 144(bỏ dấu âm)
=> x = \(\pm\)12
d) \(\frac{2x+3}{6}=\frac{x-2}{5}\)
=> 5(2x + 3) = 6(x - 2)
=> 10x + 15 = 6x - 12
=> 10x + 15 - 6x + 12 = 0
=> 4x + 27 = 0
=> 4x = -27
=> x = -27/4
e) \(\frac{x+1}{22}=\frac{6}{x}\)
=> x(x + 1) = 132
=> x(x + 1) = 11.12
=> x = 11
f) \(\frac{2x-1}{2}=\frac{5}{x}\)
=> x(2x - 1) = 10
=> 2x2 - x = 10
=> 2x2 - x - 10 = 0
tới đây tự làm đi nhé
g) \(\frac{2x-1}{21}=\frac{3}{2x+1}\)
=> (2x - 1)(2x + 1) = 63
=> 4x2 - 1 = 63
=> 4x2 = 64
=> x2 = 16
=> x = \(\pm\)4
h) Tương tự
a) \(\frac{2x+3}{15}=\frac{7}{5}\Leftrightarrow10x+15=105\Leftrightarrow10x=90\Rightarrow x=9\)
b) \(\frac{x-2}{9}=\frac{8}{3}\Leftrightarrow3x-6=72\Leftrightarrow3x=78\Rightarrow x=26\)
c) \(\frac{-8}{x}=\frac{-x}{18}\Leftrightarrow x^2=144\Leftrightarrow\orbr{\begin{cases}x=12\\x=-12\end{cases}}\)
d) \(\frac{2x+3}{6}=\frac{x-2}{5}\Leftrightarrow10x+15=12x-12\Leftrightarrow2x=27\Rightarrow x=\frac{27}{2}\)
e) \(\frac{x+1}{22}=\frac{6}{x}\Leftrightarrow x^2+x-132=0\Leftrightarrow\left(x-11\right)\left(x+12\right)=0\Leftrightarrow\orbr{\begin{cases}x=11\\x=-12\end{cases}}\)
f) \(\frac{2x-1}{2}=\frac{5}{x}\Leftrightarrow2x^2-x-10=0\Leftrightarrow\left(x-2\right)\left(2x+5\right)=0\Leftrightarrow\orbr{\begin{cases}x=2\\x=-\frac{5}{2}\end{cases}}\)
g) \(\frac{2x-1}{21}=\frac{3}{2x+1}\Leftrightarrow4x^2=64\Leftrightarrow x^2=16\Rightarrow\orbr{\begin{cases}x=4\\x=-4\end{cases}}\)
h) \(\frac{10x+5}{6}=\frac{5}{x+1}\Leftrightarrow10x^2+15x-25=0\Leftrightarrow5\left(x-1\right)\left(2x+5\right)=0\Leftrightarrow\orbr{\begin{cases}x=1\\x=-\frac{5}{2}\end{cases}}\)
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\(a,\dfrac{4}{x}=\dfrac{8}{x+1}\left(x\ne0;x\ne-1\right)\Rightarrow4x+4=8x\\ \Rightarrow x=1\\ b,\dfrac{x}{7}=\dfrac{x+16}{35}\Rightarrow35x=7x+112\\ \Rightarrow28x=112\Rightarrow x=4\\ c,\dfrac{6}{x-3}=\dfrac{7}{x-5}\left(x\ne3;x\ne5\right)\Rightarrow6x-30=7x-21\\ \Rightarrow x=-9\\ d,\dfrac{44-x}{3}=\dfrac{x-12}{5}\Rightarrow220-5x=3x-36\\ \Rightarrow8x=256\Rightarrow x=32\)