a. 2^x - 15 = 17
b. 27 . 3^x = 243
c. 3^x + 25 = 26 . 2^2 + 2 . 3^0
d. ( 7x - 11 )^3 = 2^5 . 5^2 + 200;
e. 3^x . 3 = 27
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DT
5
NN
21 tháng 6 2017
Giải:
\(a,2^x-15=17.\)
\(2^x=17+15.\)
\(2^x=32.\)
\(2^x=2^5.\)
\(\Rightarrow x=5\in N.\)
Vậy \(x=5.\)
\(b,\left(7x-11\right)^3=2^5.5^2+200.\)
\(\left(7x-11\right)^3=32.25+200.\)
\(\left(7x-11\right)^3=800+200.\)
\(\left(7x-11\right)^3=1000.\)
\(\left(7x-11\right)^3=10^3.\)
\(\Rightarrow7x-11=10.\)
\(\Rightarrow7x=10+11=21.\)
\(\Rightarrow x=21:7=3\in N.\)
Vậy \(x=3.\)
\(c,3^x+25=26.2^2+2.3^0.\)
\(3^x+25=26.2^2+2.1.\)
\(3^x+25=2\left(26.2+1\right).\)
\(3^x+25=2.53.\)
\(3^x+25=106.\)
\(3^x=106-25.\)
\(3^x=81.\)
\(3^x=3^4\Rightarrow x=4\in N.\)
Vậy \(x=4.\)
\(d,49.7^x=2041.\)(đề này sai).
Sửa đề:
\(49.7^x=2401.\)
\(7^x=2401:49.\)
\(7^x=49.\)
\(7^x=7^2\Rightarrow x=2\in N.\)
Vậy \(x=2.\)
\(e,3^x=243.\)
\(3^x=3^5\Rightarrow x=5\in N.\)
Vậy \(x=5.\)
~ Học tốt!!! ~
DH
21 tháng 6 2017
a, \(2^x-15=17\)
\(\Rightarrow2^x=32\Rightarrow2^x=2^5\)
Vì \(2\ne-1;2\ne0;2\ne1\) nên \(x=5\)
Vậy....
b, \(\left(7x-11\right)^3=2^5.5^2+200\)
\(\Rightarrow\left(7x-11\right)^3=32.25+200\)
\(\Rightarrow\left(7x-11\right)^3=1000=10^3\)
\(\Rightarrow7x-11=10\Rightarrow7x=21\Rightarrow x=3\)
Vậy.....
c, \(3^x+25=26.2^2+2.3^0\)
\(\Rightarrow3^x+25=26.4+2\)
\(\Rightarrow3^x=104+2-25\)
\(\Rightarrow3^x=81=3^4\)
Vì \(3\ne-1;3\ne0;3\ne1\) nên x=4
Vậy.....
d,Sửa đề:\(49.7^x=2401\)
\(\Rightarrow7^2.7^x=7^4\Rightarrow7^{2+x}=7^4\)
Vì \(7\ne-1;7\ne0;7\ne1\) nên \(2+x=4\Rightarrow x=2\)
Vậy.....
Câu e làm tương tự! Chúc bạn học tốt!!!
BT
2 tháng 6 2017
a) \(\dfrac{2}{3}x-\dfrac{1}{2}=\dfrac{1}{10}\)
\(\dfrac{2}{3}x=\dfrac{1}{10}+\dfrac{1}{2}=\dfrac{3}{5}\)
\(x=\dfrac{3}{5}:\dfrac{2}{3}=\dfrac{9}{10}\)
b) \(\dfrac{39}{7}:x=13\)
\(x=\dfrac{\dfrac{39}{7}}{13}=\dfrac{3}{7}\)
c) \(\left(\dfrac{14}{5}x-50\right):\dfrac{2}{3}=51\)
\(\dfrac{14}{5}x-50=51\cdot\dfrac{2}{3}=34\)
\(\dfrac{14}{5}x=34+50=84\)
\(x=\dfrac{84}{\dfrac{14}{5}}=30\)
d) \(\left(x+\dfrac{1}{2}\right)\left(\dfrac{2}{3}-2x\right)=0\)
\(\Leftrightarrow\left[{}\begin{matrix}x+\dfrac{1}{2}=0\\\dfrac{2}{3}-2x=0\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x=-\dfrac{1}{2}\\x=\dfrac{1}{3}\end{matrix}\right.\)
e) \(\dfrac{2}{3}x-\dfrac{1}{2}x=\dfrac{5}{12}\)
\(\dfrac{1}{6}x=\dfrac{5}{12}\)
\(x=\dfrac{5}{12}:\dfrac{1}{6}=\dfrac{5}{2}\)
g) \(\left(x\cdot\dfrac{44}{7}+\dfrac{3}{7}\right)\dfrac{11}{5}-\dfrac{3}{7}=-2\)
\(\left(x\cdot\dfrac{44}{7}+\dfrac{3}{7}\right)\cdot\dfrac{11}{5}=-2+\dfrac{3}{7}=-\dfrac{11}{7}\)
\(x\cdot\dfrac{44}{7}+\dfrac{3}{7}=-\dfrac{11}{7}:\dfrac{11}{5}=-\dfrac{5}{7}\)
\(\dfrac{44}{7}x=-\dfrac{5}{7}-\dfrac{3}{7}=-\dfrac{8}{7}\)
\(x=-\dfrac{8}{7}:\dfrac{44}{7}=-\dfrac{2}{11}\)
h) \(\dfrac{13}{4}x+\left(-\dfrac{7}{6}\right)x-\dfrac{5}{3}=\dfrac{5}{12}\)
\(\dfrac{25}{12}x-\dfrac{5}{3}=\dfrac{5}{12}\)
\(\dfrac{25}{12}x=\dfrac{5}{12}+\dfrac{5}{3}=\dfrac{25}{12}\)
\(x=1\)
Mỏi tay woa bn làm nốt nha!!
LN
1
15 tháng 6 2016
x^20-x=0
x(x^19-1)=0
x= 0
hoặc x ^ 19 =1
x = 0 hoặc x= 1
11 tháng 10 2020
1) \(2^x-15=17\)
\(\Leftrightarrow2^x=32=2^5\)
\(\Rightarrow x=5\)
2) \(\left(7x-11\right)^3=25\cdot5^2+200\)
\(\Leftrightarrow\left(7x-11\right)^3=825\)
\(\Leftrightarrow7x-11=\sqrt[3]{825}\)
\(\Leftrightarrow7x=11+\sqrt[3]{825}\)
\(\Rightarrow x=\frac{11+\sqrt[3]{825}}{7}\)
11 tháng 10 2020
3) \(\left(x+1\right)^{100}-3\left(x+1\right)^{99}=0\)
\(\Leftrightarrow\left(x+1\right)^{99}\left(x-2\right)=0\)
\(\Leftrightarrow\orbr{\begin{cases}\left(x+1\right)^{99}=0\\x-2=0\end{cases}}\Rightarrow\orbr{\begin{cases}x=-1\\x=2\end{cases}}\)
4) \(4x+5\left(x+3\right)=105\)
\(\Leftrightarrow9x+15=105\)
\(\Leftrightarrow9x=90\)
\(\Rightarrow x=10\)
5) \(5\cdot\left(x-2\right)+10\left(x+3\right)=170\)
\(\Leftrightarrow5\left[x-2+2\left(x+3\right)\right]=170\)
\(\Leftrightarrow3x+4=34\)
\(\Leftrightarrow3x=30\)
\(\Rightarrow x=10\)
10 tháng 4 2022
Câu 1:
a: =>-2x-x+17=34+x-25
=>-3x+17=x+9
=>-4x=-8
hay x=2
b: =>17x+16x+27=2x+43
=>33x+27=2x+43
=>31x=16
hay x=16/31
c: =>-2x-3x+51=34+2x-50
=>-5x+51=2x-16
=>-7x=-67
hay x=67/7
e: 3x-32>-5x+1
=>8x>33
hay x>33/8
RB
tìm STN x biết
a) 2x - 15 = 17
b) ( 7x - 11 )3 = 25 . 52 + 200
c) x10 = 1x
d) x10 = x
e) ( x - 1 )3 = 27
2
21 tháng 10 2015
a) 2x - 15 = 17
<=> 2x = 2
<=> x = 1
b) ( 7x - 11 )3 = 25.52 + 200
<=> ( 7x - 11 )3 = 800 + 200
<=> ( 7x - 11 )3 = 103
<=> 7x - 11 = 10
<=> 7x = 21
<=> x = 3
c) x10 = 1x
<=> x = 0 hoặc 1
d) x10 = x
<=> x = 0 hoặc 1
e) ( x - 1 )3 = 27
<=> ( x - 1 )3 = 33
<=> x - 1 = 3
<=> x = 4
a) \(2^x-15=17\)
\(2^x=17+15\)
\(2^x=32\)
\(\Rightarrow2^x=2^5\)
\(\Rightarrow x=5\)
b) \(27.3^x=243\)
\(3^x=243:27\)
\(3^x=9\)
\(\Rightarrow3^x=3^2\)
\(\Rightarrow x=2\)
c) \(3^x+25=26.2^2+2.3^0\)
\(3^x+25=104+2\)
\(3^x+25=106\)
\(3^x=106-25\)
\(3^x=81\)
\(\Rightarrow3^x=3^4\)
\(\Rightarrow x=4\)
d) \(\left(7x-11\right)^3=2^5.5^2+200\)
\(\left(7x-11\right)^3=800+200\)
\(\left(7x-11\right)^3=1000\)
\(\Rightarrow\left(7x-11\right)^3=10^3\)
\(\Rightarrow7x-11=10\)
\(7x=10+11\)
\(7x=21\)
\(x=21:7\)
\(x=3\)
e) \(3^x.3=27\)
\(3^x=27:3\)
\(3^x=9\)
\(\Rightarrow3^x=3^2\)
\(\Rightarrow x=2\)
a) \(2^x-15=17\)
\(\Leftrightarrow2^x=17+15\)
\(\Leftrightarrow2^x=32\)
\(\Leftrightarrow2^x=2^5\)
\(\Leftrightarrow x=5\)
Vậy x = 5
b) \(27.3^x=243\)
\(\Leftrightarrow3^x=243:27\)
\(\Leftrightarrow3^x=9\)
\(\Leftrightarrow3^x=3^2\)
\(\Leftrightarrow x=2\)
Vậy x = 2
c) \(\left(7x-11\right)^3=2^5.5^2+200\)
\(\Leftrightarrow\left(7x-11\right)^3=800+200\)
\(\Leftrightarrow\left(7x-11\right)^3=1000\)
\(\Leftrightarrow\left(7x-11\right)^3=10^3\)
\(\Leftrightarrow7x-11=10\)
\(\Leftrightarrow7x=10+11\)
\(\Leftrightarrow7x=21\)
\(\Leftrightarrow x=21:7\)
\(\Leftrightarrow x=3\)
Vậy x = 3
d) \(3^x.3=27\)
\(\Leftrightarrow3^x=27:3\)
\(\Leftrightarrow3^x=9\)
\(\Leftrightarrow3^x=3^2\)
\(\Leftrightarrow x=2\)
Vậy x = 2
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