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Bài 1: Tìm x biết
a) x - 50 : 25 = 8
x- 2 = 8
x= 8+2
x=10
b) (x + 40).15 = 75.24
x+40 = 75.24:15
x+40 = 70
x= 30
c) (x - 32) - 15 = 0
x- 31 = 15
x= 15+ 31
x = 46
d) 1234 : x = 2
x= 1234:2
x = 617
e) (x - 34).26 = 0
x- 34 = 0: 26
x= 0 + 34
x= 34
f) 152 + (x + 231) : 2 = 358
(x+231):2 = 358- 152
(x+231):2 = 206
x+ 231 = 206*2
x= 412 - 231
x= 181
1.
a) x - 50 : 25 = 8
x - 2 = 8
x = 10
b) (x + 40) . 15 = 75 . 24
x + 40 = 75 . 24 : 15
x + 40 = 120
x = 80
c) (x - 32) - 15 = 0
x - 32 = 15
x = 47
d) 1234 : x = 2
x = 617
e) (x - 34) . 26 = 0
Thỏa mãn điều kiện x - 34 = 0
x = 34
f) 152 + (x + 231) : 2 = 358
(x + 231) : 2 = 206
x + 231 = 412
x = 181
2.
a) 45 . (2 . x - 4) . 13 = 0
Thỏa mãn điều kiện 2 . x - 4 = 0
x = 2
b) 5 . x - 38 : 19 = 13
5 . x - 2 = 13
5 . x = 15
x = 3
c) 100 - 3 . (8 + x) = 1
3 . (8 + x) = 99
8 + x = 33
x = 25
d) [(x + 12) - 17] : 5 = 4
(x + 12) - 17 = 20
x + 12 = 37
x = 25
e) 84 - 4 . (2 . x + 1) = 48
4 . (2 . x + 1) = 36
2 . x + 1 = 9
2 . x = 8
x = 4
a) ( x-34) x 15=0
( x-34) =0 : 15
( x-34) =0
x =0 + 34
x =34
b) 18 x ( x-16)=18
( x- 16)=18 : 18
( x-16) =1
x = 16 + 1
x = 17
c) ( x-4).( x-3)=0
x . ( 4-3) =0
x . 0 =0 ( n* . o = 0 )
=> x = n*
a)(-6-18):(-4)
= { (-6) + (-8) } : (-4)
=(-24) : (-4)= (-6)
b)-28.(50-42)-35.(34-62)
= -28.8-35.(-28)
= -28.(8-35)
= -28.(-27)=756
c)-18-(-5)+26
= -18+5+26
= -13+26=13
d)-72.69+31.(-72)
= -72.(69+31)
= -72.100=-7200
Bài toán 1 : Tìm x nguyên biết.
a. 3 ≤ x – 2 < 5
=>3-2 < x-2 < 5-2
=>1 < x < 3
=>x=1
Vậy x=1
b. 0 ≤ x – 5 ≤ 2
=>0-5 < x-5 < 2-5
=>-5 < x < -3
=>x=-4
Vậy x=-4
Bài toán 2 : Tính hợp lý.
a. 4567 + (1234 – 4567) -4
=4567+1234-4567-4
=(4567-4567)+(1234-4)
=0+1230
=1230
b. 2001 – (53 + 1579) – (-53)
=2001-53-1579+53
=(2001-1579)+(-53+53)
=422+0
=422
c. 35 – 17 + 2017 – 35 + (-2017)
=(35-35)+[2017+(-2017)]-17-35
=0+0-17-35
=0-17-35
=-52
d. 37 + (-17) – 37 + 77
=(37-37)+[-17+77]
=0+60
=60
e. –(-219) + (-219) – 401 + 12
=0-401+12
=-389
f. |-85| – (-3).15
=85+3.15
=85+45
=130
g. 11.107 + 11.18 – 25.11
=11.(107+18-25)
=11.100
=1100
h. 115 – (-85) + 53 – (-500 + 53)
=115+85+53+500-53
=(53-53)+(115+85+500)
=0+700
=700
k. (-18) + (-31) + 98 + |-18| + (-69)
=-18-31+98+18-69
=(-18+18)+(-31-69)+98
=0+(-100)+98
=-100+98
=-2
Bài toán 4 : Tìm x, biêt.
a. 5x – 16 = 40 + x
5x - x = 40 + 16
4x = 56
x = 56 : 4
x=14
b. 4x – 10 = 15 – x
4x + x = 15 + 10
5x = 25
x = 25 : 5
x = 5
c. -12 + x = 5x – 20
-12 + 20 = 5x - x
8 = 4x
x = 8 : 4
x = 2
d. 7x – 4 = 20 + 3x
7x - 3x = 20 + 4
4x=24
x=24:4
x=6
e. 5x – 7 = – 21 – 2x
5x + 2x = -21+7
7x = -14
x = -14 : 7
x = -2
f. x + 15 = 7 – 6x
x + 6x = 7 - 15
7x = -8
x = -8/7
g. 17 – x = 7 – 6x
17 - 7 = -6x + x
10 = -7x
x=10/-7
h. 3x + (-21) = 12 – 8x
3x + 8x = 12 + 21
11x = 33
x = 33:11
x=3
k. 125 : (3x – 13) = 25
3x-13=125:25
3x-13=5
3x=5+13
3x=18
x=18:3
x=6
l. 541 + (218 – x) = 735
218-x=735-541
218-x=693
x=218-693
x=-475
Bài 1 Tìm x biết:
a)65-(29-x)=32
65 -29+x=31
x=31-65+29
x=-5
b)(x+5)-(x+23)=x-34
x+5 -x +23 = x-34
(x-x)+ (23+5)=x-34
0+28=x-34
28=x-34
28+34=x
62=x
=>x=62
c)(16-x)+(x-38)=x+44
16-x+x-38=x+44
-x+x-x=44-16+38
-x=36
=>x=-36
d)-12+3(-x+7)=-18
3(-x+7)=-18+12
3(-x+7)=-6
-x+7=-6:3
-x+7=-2
-x=-2-7
-x=-9
=>x=9
Baif 2
d)|7-x|=10
=> \(\left[{}\begin{matrix}7-x=10\\7-x=-10\end{matrix}\right.\)
\(\Rightarrow\)\(\left[{}\begin{matrix}x=7-10\\x=-10-7\end{matrix}\right.\)
\(\Rightarrow\)\(\left[{}\begin{matrix}x=-3\\x=-17\end{matrix}\right.\)
e)(x-6).(7-2x)=0
\(\Rightarrow\)\(\left[{}\begin{matrix}x-6=0\\7-2x=0\end{matrix}\right.\)
\(\Rightarrow\)\(\left[{}\begin{matrix}x=0+6\\2x=7\end{matrix}\right.\)
\(\Rightarrow\)\(\left[{}\begin{matrix}x=6\\x=7:2\end{matrix}\right.\)
\(\Rightarrow\)\(\left[{}\begin{matrix}x=6\\x=3,5\end{matrix}\right.\)
f)(9-x).(2x+8)=0
\(\Rightarrow\)\(\left[{}\begin{matrix}9-x=0\\2x+8=0\end{matrix}\right.\)
\(\Rightarrow\)\(\left[{}\begin{matrix}x=0+9\\2x=-8\end{matrix}\right.\)
\(\Rightarrow\)\(\left[{}\begin{matrix}x=9\\x=-4\end{matrix}\right.\)
g)x(-x+8).(-3x-18)=0
\(\Rightarrow\) \(\left[{}\begin{matrix}x=0\\-x+8=0\\-3x-18=0\end{matrix}\right.\)
\(\Rightarrow\)\(\left[{}\begin{matrix}x=0\\-x=0+8\\-3x=0+18\end{matrix}\right.\)
\(\Rightarrow\)\(\left[{}\begin{matrix}x=0\\-x=8\\-3x=18\end{matrix}\right.\)
\(\Rightarrow\)\(\left[{}\begin{matrix}x=0\\x=-8\\x=18:\left(-3\right)\end{matrix}\right.\)
\(\Rightarrow\)\(\left[{}\begin{matrix}x=0\\x=-8\\x=-6\end{matrix}\right.\)
h)(-x+8).(x-54).(-24-x)=0
\(\Rightarrow\)\(\left[{}\begin{matrix}-x+8=0\\x-54=0\\-24-x=0\end{matrix}\right.\)
\(\Rightarrow\)\(\left[{}\begin{matrix}-x=8\\x=0+54\\-x=0+24\end{matrix}\right.\)
\(\Rightarrow\)\(\left[{}\begin{matrix}x=8\\x=54\\-x=24\end{matrix}\right.\)
\(\Rightarrow\)\(\left[{}\begin{matrix}x=8\\x=54\\x=-24\end{matrix}\right.\)
c) 2x - 49 = 5 . 32
2x - 49 = 5 . 9
2x - 49 = 45
2x = 45 + 49
2x = 94
x = 94 : 2
x = 47
a ) đề là x + 5 = 23 đúng ko
x = 18
b ) x = 32
c ) x = 12
d ) x = 7
e ) x = 34
f ) x = 17
g ) x = 135
h ) x = 1
Xin lỗi nha bài a) x + 5 = 23 mới đúng !