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\(a,2\frac{x}{7}=\frac{75}{35}\)
\(\frac{75}{35}=2\frac{5}{35}=2\frac{1}{7}\)
\(\Rightarrow x=1\)
\(b,47:4=...\left(+3\right)\)
\(\Rightarrow\left(47-3\right):4=11\)
\(\Rightarrow x=11\)
\(c,\frac{112}{5}=\frac{336}{15}=22\left(+6\right)\)
\(\Rightarrow x=22\frac{x=6}{15}\)
\(d,7,5x=\frac{75x}{100}:\left(9-6\frac{13}{21}\right)=2\frac{13}{25}\)
\(\frac{75x}{100}:\left(9-\frac{139}{21}\right)=\frac{63}{25}\)
\(\frac{75x}{100}:\frac{50}{21}=\frac{63}{25}\)
\(\Rightarrow\frac{63^3}{25^{\left(1\right)}}\cdot\frac{50^{\left(2\right)}}{21^1}=6=\frac{6}{1}\)
\(\Rightarrow\frac{6}{1}=\frac{600}{100}\)
Con d sai đề
Lời giải:
a)
\(|x|=2019\Rightarrow \left[\begin{matrix} x=2019\\ x=-2019\end{matrix}\right.\)
b)
\(|x-3|=21\Rightarrow \left[\begin{matrix} x-3=21\\ x-3=-21\end{matrix}\right.\Rightarrow \left[\begin{matrix} x=24\\ x=-18\end{matrix}\right.\)
c)
\(|x|-25+x=9\)
\(\Leftrightarrow |x|+x=34\)
Nếu $x\geq 0$: $|x|=x$
\(\Rightarrow x+x=34\Rightarrow 2x=34\Rightarrow x=17\) (thỏa mãn)
Nếu $x< 0$: $|x|=-x$
$\Rightarrow -x+x=34\Rightarrow 0=34$ (vô lý -loại)
Vậy $x=17$
d) \(|x-2|+2x=4\)
Nếu $x\geq 2\Rightarrow |x-2|=x-2$
$\Rightarrow x-2+2x=4\Rightarrow 3x=6\Rightarrow x=2$ (thỏa mãn)
Nếu $x< 2\Rightarrow |x-2|=2-x$
$\Rightarrow 2-x+2x=4\Rightarrow x=2$ (loại vì $x< 2$)
Vậy $x=2$
e)
$|x-5|+3x+2=13$
Nếu $x\geq 5$ thì $|x-5|=x-5$
\(\Rightarrow x-5+3x+2=13\)
\(\Leftrightarrow 4x=16\Leftrightarrow x=4\) (loại vì $x\geq 5$)
Nếu $x< 5$ thì $|x-5|=5-x$
$\Rightarrow 5-x+3x+2=13$
$\Leftrightarrow 2x=6\Rightarrow x=3$ (thỏa mãn)
Vậy $x=3$
d) 4x.4 + 4x = 320
4x.(4+1) = 320
4x.5 = 320
4x = 320 : 5
4x = 64 = 43
=> x = 3
e) 5x+3+5x = 630
5x.53+5x = 630
5x.(53+1) = 630
5x.126 = 630
5x = 630 : 126
5x = 5 =51
=> x = 1
g) 9x=274
(32)x = (33)4
32x = 312
=> 2x = 12
x = 6
a) 3x -18 = 0
3x = 18
=> không tìm được x
b) 4.5x =100
5x =100 : 4
5x = 25 = 52
=> x = 2
c) 3x:32=94
3x-2 = (32)4 =38
=> x- 2 = 8
x = 10
Bài 1: Tính ( hợp lý nếu có thể )
\(A=\dfrac{-3}{8}+\dfrac{12}{25}+\dfrac{5}{-8}+\dfrac{2}{-5}+\dfrac{13}{25}\)
\(=\left(\dfrac{-3}{8}+\dfrac{5}{-8}\right)+\left(\dfrac{12}{25}+\dfrac{13}{25}\right)+\dfrac{2}{-5}\)
\(=-1+1+\dfrac{2}{-5}\)
\(=0+\dfrac{2}{-5}\)
\(=\dfrac{2}{-5}\)
\(B=\dfrac{-3}{15}+\left(\dfrac{2}{3}+\dfrac{3}{15}\right)\)
\(=\left(\dfrac{-3}{15}+\dfrac{3}{15}\right)+\dfrac{2}{3}\)
\(=0+\dfrac{2}{3}\)
\(=\dfrac{2}{3}\)
\(C=\dfrac{-5}{21}+\left(\dfrac{-16}{21}+1\right)\)
\(=\left(\dfrac{-5}{21}+\dfrac{-16}{21}\right)+1\)
\(=-1+1\)
\(=0\)
\(D=\left(\dfrac{-1}{6}+\dfrac{5}{-12}\right)+\dfrac{7}{12}\)
\(=\left(\dfrac{5}{-12}+\dfrac{7}{12}\right)+\dfrac{-1}{6}\)
\(=\dfrac{1}{6}+\dfrac{-1}{6}\)
\(=0\)
Bài 2: Tìm x,biết:
a) \(x+\dfrac{2}{3}=\dfrac{4}{5}\)
\(x=\dfrac{4}{5}-\dfrac{2}{3}\)
\(x=\dfrac{2}{15}\)
Vậy \(x=\dfrac{2}{15}\)
b) \(x-\dfrac{2}{3}=\dfrac{7}{21}\)
\(\Rightarrow x-\dfrac{2}{3}=\dfrac{1}{3}\)
\(x=\dfrac{1}{3}+\dfrac{2}{3}\)
\(x=\dfrac{3}{3}=1\)
Vậy \(x=1\)
c) sai đề hay sao ấy bạn.bỏ dấu - ở x thì đúng đề.mk giải luôn nha!
\(x-\dfrac{3}{4}=\dfrac{-8}{11}\)
\(x=\dfrac{-8}{11}+\dfrac{3}{4}\)
\(x=\dfrac{1}{44}\)
Vậy \(x=\dfrac{1}{44}\)
d) \(\dfrac{11}{12}-\left(\dfrac{2}{5}+x\right)=\dfrac{2}{3}\)
\(\dfrac{2}{5}+x=\dfrac{11}{12}-\dfrac{2}{3}\)
\(\dfrac{2}{5}+x=\dfrac{1}{4}\)
\(x=\dfrac{1}{4}-\dfrac{2}{5}\)
\(x=-\dfrac{3}{20}\)
Vậy \(x=-\dfrac{3}{20}\)
a) 2x . 4 = 128
2x = 128 : 4
2x = 32
2x = 25
=> x = 5
b) 2x . 24 = 26
=> x + 4 = 6
x = 6 - 4
x = 2
c) 5x + x = 39 - 311 : 39
6x = 39 - 32
6x = 39 - 9
6x = 30
x = 30 : 6
x = 5
d) 9x - 1 = 81
9x - 1 = 92
=> x - 1 = 2
x = 2 + 1
x = 3
e) 6x = 521 : 519 + 3 . 22 - 70
6x = 52 + 3 . 4 - 1
6x = 25 + 12 - 1
6x = 37 - 1
6x = 36
x = 36 : 6
x = 6
\(-\frac{9}{11}\cdot\frac{3}{8}-\frac{9}{11}\cdot\frac{5}{8}+\frac{17}{11}=-\frac{9}{11}\left(\frac{3}{8}+\frac{5}{8}\right)+\frac{17}{11}=-\frac{9}{11}\cdot1+\frac{17}{11}=1\)
\(\frac{2}{1.3}+....+\frac{2}{53.55}=1-\frac{1}{3}+\frac{1}{3}-\frac{1}{5}+...+\frac{1}{53}-\frac{1}{55}=1-\frac{1}{55}=\frac{54}{55}\)
\(x+5-\frac{1}{2}=3\frac{1}{2}\)
\(x+5=3.5+0.5=4\)
\(x=4-5=-1\)
\(3^{x+1}=27=3^3\)
\(x+1=3\)
vậy x=2
a, \(5^x=625\Rightarrow5^x=5^4\Rightarrow x=4\)
b, \(4^{2x-6}=1\Rightarrow4^{2x-6}=4^0\)
\(\Rightarrow2x-6=0\Rightarrow x=3\)
c, \(\left(3x-1\right)^3=8\Rightarrow3x-1=2\)
\(\Rightarrow x=1\)
d, \(49.7^n=2401\Rightarrow7^{n+2}=7^4\)
\(\Rightarrow n+2=4\Rightarrow n=2\)
e, \(x^4.x-27.x=0\)
\(\Rightarrow x\left(x^4-27\right)=0\)
\(\Rightarrow\orbr{\begin{cases}x=0\\x^4-27=0\end{cases}}\Rightarrow\orbr{\begin{cases}x=0\\x=\pm\sqrt[4]{27}\end{cases}}\)
f, \(\left(x-6\right)^3=\left(x-6\right)^2\)
\(\Rightarrow\left(x-6\right)^3-\left(x-6\right)^2=0\)
\(\Rightarrow\left(x-6\right)^2\left(x-6-1\right)=0\)
\(\Rightarrow\orbr{\begin{cases}x-6=0\\x-7=0\end{cases}}\Rightarrow\orbr{\begin{cases}x=6\\x=7\end{cases}}\)
Chúc bạn học tốt!!!
\(a,5^x=625\) \(b,4^{2x-6}=1\)
\(\Rightarrow5^x=5^4\) \(\Rightarrow2x-6=0\) (Vì mọi số mũ không bằng 1)
\(\Rightarrow x=4\) \(\Rightarrow2x=6\)
\(\Rightarrow x=3\)
\(c,\left(3x-1\right)^3=8\) \(d,49.7^n=2401\)
\(\Rightarrow\left(3x-1\right)^3=2^3\) \(\Rightarrow7^n=2401:49\)
\(\Rightarrow3x-1=2\) \(\Rightarrow7^n=49\)
\(\Rightarrow3x=3\) \(\Rightarrow7^n=7^2\)
\(\Rightarrow x=1\) \(\Rightarrow n=2\)
\(e,x^4.x-27.x=0\)
\(\Rightarrow x.\left(x^4-27\right)=0\)
\(\Rightarrow\hept{\begin{cases}x=0\\x^4-27=0\end{cases}\Rightarrow\hept{\begin{cases}x=0\\x^4=27\end{cases}}}\)
\(f,\left(x-6\right)^3=\left(x-6\right)^2\)
\(\Rightarrow x.\left(x^4-27\right)=0\) \(\Rightarrow\hept{\begin{cases}\left(x-6\right)^3=\left(x-6\right)^2\\\left(x-6\right)^3=\left(x-6\right)^2\end{cases}\Rightarrow\hept{\begin{cases}\left(x-6\right)^3:\left(x-6\right)^2=1\\\left(x-6\right)^3-\left(x-6\right)^2=0\end{cases}\Rightarrow}\hept{\begin{cases}x-6=1\\x-6=0\end{cases}}\Rightarrow\hept{\begin{cases}x=7\\x=6\end{cases}}}\)
\(A=\left|-x+8\right|-21\)
\(A=\left|-x+8\right|-21\ge-21\)
\(MinA=-21\Leftrightarrow-x+8=0\)\(\Leftrightarrow x=8\)
\(B=\left|-x-17\right|+\left|y-36\right|+12\)
\(B=\left|-x-17\right|+\left|y-36\right|+12\ge12\)
\(MinB=12\Leftrightarrow\hept{\begin{cases}-x-17=0\\y-36=0\end{cases}}\Leftrightarrow\hept{\begin{cases}x=-17\\y=36\end{cases}}\)
\(C=-\left|2x+8\right|-35\)
\(C=-\left|2x+8\right|-35\le-35\)
\(MaxC=-35\Leftrightarrow2x+8=0\Leftrightarrow x=-4\)
a) \(320 : x = 16\)
⇒ \(x = 320 : 16 = 20\)
x = 20
b) \(x \times 13 = 11\)
⇒ \(x = 11 : 13\)
x = 11/13
c) \(x : 25 = 112\)
⇒ \(x = 112 \times 25 = 2800\)
x = 2800
d) \(x - 27 : 3 = 2\)
Tính trước: \(27 : 3 = 9\)
⇒ \(x - 9 = 2\)
⇒ \(x = 11\)
x = 11
e) \(21 - 3 \times x = 6\)
⇒ \(3 x = 21 - 6\)
⇒ \(3 x = 15\)
⇒ \(x = 5\)
x = 5
Đáp án:
a) 20
b) 11/13
c) 2800
d) 11
e) 5
a) 320 : x = 16
x = 320 : 16
x = 20
Vậy x = 20
b) x13 = 11
x = 11/13
Vậy x = 11/13
c) x : 25 = 112
x = 112 . 25
x = 2800
Vậy x = 2800
d) x - 27 : 3 = 2
x - 9 = 2
x = 2 + 9
x = 11
Vậy x = 11
e) 21 -3x = 6
3x = 21 - 6
3x = 15
x = 15 : 3
x = 5
Vậy x = 5
a) \(320:x=\) \(16\)
\(x=320:16\)
\(x=20\)
Vậy \(x\) = 20
b) \(x\) x 13 = 11
\(x\) = 11:13
\(x\) = \(\frac{11}{13}\)
Vậy \(x=\frac{11}{13}\)
c) \(x\) :25 =112
\(x\) = 112 x 25
\(x\) = 2800
Vậy \(x\) = 2800
d) \(x\) - 27:3 = 2
\(x\) - 9 = 2
\(x\) = 2+9
\(x\) = 11
Vậy \(x\) = 11
e) \(21-3\times x=621\)
\(3x=21-621\)
\(3x=-600\)
\(x=-600:3\)
\(x\) = -200
Vậy \(x=-200\)
Câu a.
320 : x = 16
x = 320 : 16
x = 20
Câu b.
x - 13 = 11
x = 11 + 13
x = 24
Câu c.
x : 25 = 112
x = 112 × 25
x = 2800
Câu d.
x - 27 : 3 = 2
x - 9 = 2
x = 11
Câu e.
21 - 3x = 6
3x = 21 - 6
3x = 15
Mình giải từng câu theo cách hiểu chuẩn toán tiểu học (dấu “:” là phép chia):
A. \(320 : x = 16\)
→ \(320 / x = 16\)
→ \(320 = 16 x\)
→ \(x = 320 / 16 = 20\)
B. \(x 13 = 11\) (hiểu là \(x : 13 = 11\))
→ \(x / 13 = 11\)
→ \(x = 11 \times 13 = 143\)
C. \(x : 25 = 112\)
→ \(x / 25 = 112\)
→ \(x = 112 \times 25 = 2800\)
D. \(x - 27 : 3 = 2\) (hiểu là \(x - \left(\right. 27 / 3 \left.\right) = 2\))
→ \(27 / 3 = 9\)
→ \(x - 9 = 2\)
→ \(x = 11\)
E. Phần này bạn gõ hơi lỗi:
21-3x χ χ =6Nếu hiểu là: \(21 - 3 x = 6\)
→ \(- 3 x = 6 - 21 = - 15\)
→ \(x = 5\)
Nếu bạn muốn, bạn có thể chụp lại đề hoặc gõ lại câu E rõ hơn, mình kiểm tra giúp cho chắc chắn.
a.
320 : x = 16
x = 320 : 16
x = 20
Vậy x = 20, vì 320 : 20 = 16.
b.
x : 13 = 11
x = 11 × 13
x = 143
Vậy x = 143, vì 143 : 13 = 11.
c.
x : 25 = 112
x = 112 × 25
x = 2800
Vậy x = 2800, vì 2800 : 25 = 112.
d.
x - 27 : 3 = 2
x - 9 = 2
x = 11
Vậy x = 11, vì 27 : 3 = 9.