tim x tnuoc N biết :
a, (3x - 4). 23 = 64
b. 23 . 32 - 4x = 43
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a. ( 3x - 4 ) . 23 = 64
( 3x - 4 ) . 2 = 4
3x - 4 = 2
3x = 6
x= 2
b. 2x = 32
2x = 25
x = 5
a, 70 - 5 ( x - 3 ) = 45
⇔ 5 . x - 3 = 70 - 45
⇔ 5 x - 3 = 35
⇔ x - 3 = 35 : 5 ⇔ x - 3 = 7
⇔ x = 10
b, 10 + 2 x = 4 5 : 4 3
⇔ 10 + 2 x = 4 2 ⇔ 10 + 2 x = 16
⇔ 2 x = 4 ⇔ x = 2
c, 60 - 3 x - 2 = 51
⇔ 3 x - 2 = 60 - 51
⇔ 3 x - 2 = 9
⇔ x - 2 = 3 ⇔ x = 5
d, 4 x - 20 = 2 5 : 2 3
⇔ 4 x - 20 = 2 2 ⇔ 4 x - 20 = 4
⇔ 4 x = 24 ⇔ x = 6
a: \(280-\left(x-140\right):35=270\)
=>(x-140):35=280-270=10
=>x-140=350
=>x=350+140
=>x=490
b: \(\left(190-2x\right):35-32=16\)
=>\(\left(190-2x\right):35=32+16=48\)
=>\(190-2x=35\cdot48=1680\)
=>2x=190-1680=-1490
=>x=-745
c: \(720:\left\lbrack41-\left(2x-5\right)\right\rbrack=2^3\cdot5\)
=>\(720:\left\lbrack41-\left(2x-5\right)\right\rbrack=8\cdot5=40\)
=>41-(2x-5)=720:40=18
=>2x-5=41-18=23
=>2x=28
=>x=14
d: \(\left(x:23+45\right)\cdot37-22=2^4\cdot105\)
=>\(\left(\frac{x}{23}+45\right)\cdot37=16\cdot105+22=1702\)
=>\(\frac{x}{23}+45=46\)
=>\(\frac{x}{23}=1\)
=>x=23
e: \(\left(3x-4\right)\left(x-1\right)^3=0\)
=>\(\left[\begin{array}{l}3x-4=0\\ x-1=0\end{array}\right.\Rightarrow\left[\begin{array}{l}x=\frac43\\ x=1\end{array}\right.\)
f: \(2^{2x-1}:4=8^3\)
=>\(2^{2x-1-2}=2^9\)
=>2x-3=9
=>2x=12
=>x=6
g: \(x^{17}=x\)
=>\(x^{17}-x=0\)
=>\(x\left(x^{16}-1\right)=0\)
=>\(\left[\begin{array}{l}x=0\\ x^{16}-1=0\end{array}\right.\Rightarrow\left[\begin{array}{l}x=0\\ x^{16}=1\end{array}\right.\Rightarrow\left[\begin{array}{l}x=0\\ x=1\\ x=-1\end{array}\right.\)
h: \(\left(x-5\right)^4=\left(x-5\right)^6\)
=>\(\left(x-5\right)^6-\left(x-5\right)^4=0\)
=>\(\left(x-5\right)^4\cdot\left\lbrack\left(x-5\right)^2-1\right\rbrack=0\)
=>\(\left(x-5\right)^4\cdot\left(x-4\right)\left(x-6\right)=0\)
=>x∈{4;5;6}
i: \(\left(x+2\right)^5=2^{10}\)
=>\(\left(x+2\right)^5=\left(2^2\right)^5=4^5\)
=>x+2=4
=>x=2
k: 1+2+3+...+x=78
=>\(\frac{x\left(x+1\right)}{2}=78\)
=>x(x+1)=156
=>\(x^2+x-156=0\)
=>(x+13)(x-12)=0
=>x=-13(loại) hoặc x=12(nhận)
l: \(\left(3x-2^4\right)\cdot7^3=2\cdot7^4\)
=>\(3x-16=2\cdot\frac{7^4}{7^3}=2\cdot7=14\)
=>3x=16+14=30
=>\(x=\frac{30}{3}=10\)
n: \(5^{x}:5^2=125\)
=>\(5^{x-2}=5^3\)
=>x-2=3
=>x=5
m: \(\left(x+1\right)^2=\left(x+1\right)^0\)
=>\(\left(x+1\right)^2=1\)
=>\(\left[\begin{array}{l}x+1=1\\ x+1=-1\end{array}\right.\Rightarrow\left[\begin{array}{l}x=0\\ x=-2\end{array}\right.\)
o: Số số hạng của dãy số 2;4;..;52 là:
(52-2):2+1=50:2+1=25+1=26(số)
Tổng của dãy số 2;4;...;52 là:
\(\left(52+2\right)\cdot\frac{26}{2}=54\cdot13=702\)
(2+x)+(4+x)+...+(52+x)=780
=>26x+702=780
=>26x=78
=>x=3
p: \(70=2\cdot5\cdot7;80=2^4\cdot5\)
=>ƯCLN(70;80)=\(2\cdot5=10\)
70⋮x; 80⋮x
=>x∈ƯC(70;80)
=>x∈Ư(10)
mà x>8
nên x=10
q: \(12=2^2\cdot3;25=5^2;30=2\cdot3\cdot5\)
=>BCNN(12;25;30)=\(2^2\cdot3\cdot5^2=300\)
x⋮12; x⋮25; x⋮30
=>x∈BC(12;25;30)
=>x∈B(300)
mà 0<x<500
nên x=300
45 x 32 + 45 x 23
= 45 x ( 32 + 23 )
= 45 x 55
= 2475
45 : 32 + 45 : 23
= 1,40625 + 1,9566521739
= 3,362771739
43 x 33 + 43 x 22 + 43
= 43 x ( 33 + 22 + 1 )
= 43 x 56
= 2408
45 x 32 + 45 x 23
= 45 x ( 32 + 23 )
= 45 x 55
= 2475
45 : 32 + 45 : 23
= 1,40625 + 1,9566521739
= 3,362771739
43 x 33 + 43 x 22 + 43
= 43 x ( 33 + 22 + 1 )
= 43 x 56
= 2408
a, x - 1 2 = 36
ó x - 1 2 = 6 2
ó x – 1 = 6
ó x = 7
Vậy x = 7
b, 7 x - 11 3 = 2 5 . 5 2 + 200
=> 7 x - 11 3 = 800 + 200
=> 7 x - 11 3 = 1000
=> 7 x - 11 3 = 10 3
=> 7x – 11 = 10
=> 7x = 21
=> x = 3
Vậy x = 3
c, x 11 = x
=> x 11 - x = 0
=> x ( x 10 - 1 ) = 0
=>
d, x 2 = 2 3 + 3 2 + 4 3
=> x 2 = 81
=> x = 9
e, 2 x 3 3 2 = 48
=> 2 x 3 9 = 48
=> 2 x 3 = 48 . 9
=> x 3 = 216
=> x 3 = 6 3
=> x = 6
f, 2 x + 1 3 = 125
=> 2 x + 1 3 = 5 3
=> 2x + 1 = 5
=> 2x = 4
=> x = 2
a,\(\left(3x-4\right).2^3=64\)
(=) \(\left(3x-4\right)=64:8\)
(=) \(3x-4=8\)
(=) \(3x=8+4\)
(=) \(3x=12\)
(=) \(x=12:3\)
(=) \(x=4\)
b, Ta có \(2^3.3^2-4x=4^3\)
(=) \(8.9-4x=64\)
(=) \(72-4x=64\)
(=) \(4x=72-64\)
(=) \(4x=8\)
(=) \(x=8:4\)
(=) \(x=2\)
a) ( 3x - 4 ) . 23 = 64
=> ( 3x - 4 ) = 64 : 23
=> ( 3x - 4 ) = 26 : 23
=> ( 3x - 4 ) = 23
=> 3x - 4 = 8
=> 3x = 12
=> x = 4
b) 23 . 32 - 4x = 43
=> 8 . 9 - 4x = 64
=> 72 - 4x = 64
=> 4x = 8
=> x = 2