315+(125-5x)=435
575-(6x+70)=445
228-28.( x+4)=32
(9x+2).3+1=61
720: [ 41-(x-5)] -5 =35
(24+5x).71=75
(20+4x).82003=82005
3x-16=2.74:73
x3=27
3x=81
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Bài 1
S₂ = 21 + 23 + 25 + ... + 1001
Số số hạng của S₂:
(1001 - 21) : 2 + 1 = 491
⇒ S₂ = (1001 + 21) . 491 : 2 = 250901
--------
S₄ = 15 + 25 + 35 + ... + 115
Số số hạng của S₄:
(115 - 15) : 10 + 1 = 11
⇒ S₄ = (115 + 15) . 11 : 2 = 715
Bài 2
a) 2x - 138 = 2³.3²
2x - 138 = 8.9
2x - 138 = 72
2x = 72 + 138
2x = 210
x = 210 : 2
x = 105
b) 5.(x + 35) = 515
x + 35 = 515 : 5
x + 35 = 103
x = 103 - 35
x = 78
c) 814 - (x - 305) = 712
x - 305 = 814 - 712
x - 305 = 102
x = 102 + 305
x = 407
d) 20 - [7.(x - 3) + 4] = 2
7(x - 3) + 4 = 20 - 2
7(x - 3) + 4 = 18
7(x - 3) = 18 - 4
7(x - 3) = 14
x - 3 = 14 : 7
x - 3 = 2
x = 2 + 3
x = 5
e) 9ˣ⁻¹ = 9
x - 1 = 1
x = 1 + 1
x = 2
18 - 4\(x\) = -20 - 6\(x\)
-4\(x\) + 6\(x\) = - 20 - 18
2\(x\) = - 38
\(x\) = - 19
h, -15 \(\times\) 24 = -7\(x\) + 32
7\(x\) = 360 + 32
7\(x\) = 392
\(x\) = 392:7
\(x\) = 56
i, 15\(x\) -3.(4\(x\) - 6) = -12 + 36
15\(x\) - 12\(x\) + 18 = 24
3\(x\) = 24 - 18
3\(x\) = 6
\(x\) = 2
k, -10\(x\) - 27 = -7\(x\) + 33
-27 - 33 = -7\(x\) + 10\(x\)
3\(x\) = -60
\(x\) = -20
a: Ta có: \(7x+25=144\)
\(\Leftrightarrow7x=119\)
hay x=17
b: Ta có: \(33-12x=9\)
\(\Leftrightarrow12x=24\)
hay x=2
c: Ta có: \(128-3\left(x+4\right)=23\)
\(\Leftrightarrow3\left(x+4\right)=105\)
\(\Leftrightarrow x+4=35\)
hay x=31
d: Ta có: \(71+\left(726-3x\right)\cdot5=2246\)
\(\Leftrightarrow5\left(726-3x\right)=2175\)
\(\Leftrightarrow726-3x=435\)
\(\Leftrightarrow3x=291\)
hay x=97
e: Ta có: \(720:\left[41-\left(2x+5\right)\right]=40\)
\(\Leftrightarrow41-\left(2x+5\right)=18\)
\(\Leftrightarrow2x+5=23\)
\(\Leftrightarrow2x=18\)
hay x=9
a) \(2\left(3x-4\right)=18\Leftrightarrow3x-4=9\)
\(\Leftrightarrow3x=13\Rightarrow x=\frac{13}{3}\)
b) \(\left(105-x\right)\div25=30+1\)
\(\Leftrightarrow105-x=775\)
\(\Leftrightarrow x=-670\)
c) \(2x-138=22.32\)
\(\Leftrightarrow x-69=11.32\)
\(\Leftrightarrow x-69=352\)
\(\Rightarrow x=421\)
d) \(\left(6x-9\right).28=5628\)
\(\Leftrightarrow\left(2x-3\right).84=5628\)
\(\Leftrightarrow2x-3=67\)
\(\Leftrightarrow2x=70\)
\(\Rightarrow x=35\)
e) \(\left(9x+2\right).3=60\)
\(\Leftrightarrow9x+2=20\)
\(\Leftrightarrow9x=18\)
\(\Rightarrow x=2\)
g) \(\left(26-3x\right)\div5+71=75\)\(\Leftrightarrow26-3x=20\)
\(\Leftrightarrow3x=6\)
\(\Rightarrow x=2\)
h) \(5x+1=125\)
\(\Leftrightarrow5x=124\)
\(\Rightarrow x=\frac{124}{5}\)
i) \(\left(x-5\right)\left(2x+8\right)=0\)
\(\Leftrightarrow\orbr{\begin{cases}x-5=0\\2x+8=0\end{cases}}\Leftrightarrow\orbr{\begin{cases}x=5\\2x=-8\end{cases}}\Leftrightarrow\orbr{\begin{cases}x=5\\x=-4\end{cases}}\)
1: \(\dfrac{2x^3+11x^2+18x-3}{2x+3}\)
\(=\dfrac{2x^3+3x^2+8x^2+12x+6x+9-12}{2x+3}\)
\(=x^2+4x+3-\dfrac{12}{2x+3}\)
18x -19 = 21 + 8x
18 x - 8x = 21 + 19
10 x = 40
x =4
g) 18 -4x=-20-6x
-4x + 6x = -20 - 18
2x = -38
x= -19
k, -10 \(x\) - 27 = -7\(x\) + 33
-27 - 33 = -7\(x\) + 10\(x\)
3\(x\) = -60
\(x\) - 20
m, -17\(x\) - 24 = -9\(x\) - 40
-24 + 40 = -9\(x\) + 17\(x\)
8\(x\) = 16
\(x\) = 2