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a) 150 : [17 - (2x - 3)] = 350
=> 17 - (2x - 3) = \(\frac{150}{350}=\frac{3}{7}\)
=> 2x - 3 = \(17-\frac{3}{7}=\frac{116}{7}\)
=> 2x = \(\frac{116}{7}+3\)
=> 2x = \(\frac{137}{7}\)
=> x = \(\frac{137}{7}:2=\frac{137}{14}\)
b) 4 . [105 - (x - 9)] - 486 = 0
=> 4. [105 - (x - 9)] = 486
=> 105 - (x - 9) = 243/2
=> x - 9 = \(105-\frac{243}{2}=-\frac{33}{2}\)
=> x = \(-\frac{33}{2}+9=-\frac{15}{2}\)
c) 1000 - 2{600 - 4.[198 - 7.(21 - 7)]}.x = 200
=> 1000 - 2{600 - 4.[198 - 7.14]}.x = 200
=> 1000 - 2{600 - 4.[198 - 98].x = 200
=> 1000 - 2{600 - 4.100}.x = 200
=> 1000 - 2{600 -400}.x = 200
=> 1000 - 2.200.x = 200
=> 2.200.x = 800
=> 400.x = 800
=> x = 2
Câu 2 :
a) 350 : [19 - (7x - 3)] = 350
=> 19 - (7x - 3) = 1
=> 7x - 3 = 18
=> 7x = 21
=> x = 3
b) 7.[109 - (x - 9)] - 420 = 0
=> 7.[109 - (x - 9)] = 420
=> 109 - (x - 9) = 60
=> x - 9 = 49
=> x = 49 + 9 = 58
c) 254 - 2{200 - 4.[90 - 7.(19 - 9)]}.x = 54
=> 254 - 2{200 - 4.[90 - 7.10]}.x = 54
=> 254 - 2{200 - 4[90 - 70]} . x= 54
=> 254 - 2{200 - 4.20} . x = 54
=> 254 - 2{200 - 80}.x = 54
=> 254 - 2.120 . x= 54
=> 2.120.x = 200
=> 240.x = 200
=> \(x=\frac{5}{6}\)
\(\text{a)}350:\left[19-\left(7x-3\right)\right]=350\)
\(\Rightarrow19-\left(7x-3\right)=1\)
\(\Rightarrow19-7x+3=1\)
\(\Rightarrow-7x=-21\)
\(\Rightarrow x=3\)
\(\text{b)}7.\left[109-\left(x-9\right)\right]-420=0\)
\(\Rightarrow7\left(109-x+9\right)=420\)
\(\Rightarrow118-x=60\)
\(\Rightarrow x=58\)
\(\text{c)}252-2\left\{200-4\left[90-7.\left(19-9\right)\right]\right\}.x=4\)
\(\Rightarrow2\left\{200-4\left[90-7.10\right]\right\}.x=250\)
\(\Rightarrow\left[200-4\left(90-70\right)\right].x=125\)
\(\Rightarrow\left[200-4.20\right].x=125\)
\(\Rightarrow120x=125\)
\(\Rightarrow x=\frac{125}{120}=\frac{25}{24}\)
\(\text{Xin điểm ạ}\)
350:[19-(7x-3)]=350
[19-(7x-3)]=350:350
[19-(7x-3)]=1
(7x-3)=19-1
(7x-3)=18
7x=18+3
7x=21
x=21:7
x=3
vậy x=3
7.[109-(x-19)]-420=0
7.[109-(x-19)]=0+420
7.[109-(x-19)]=420
[109-(x-19)]=420:7
[109-(x-19)]=60
(x-19)=109-60
(x-19)=49
x=49+19
x=58
vậy x=58
254-2{200-4.[90-7.(19-9)]}.x=4
254-2{200-4.[90-7.10]}.x=4
254-2{200-4.[90-70]}.x=4
254-2{200-4.20}.x=4
254-2{200-80}.x=4
254-2.120.x=4
254-240.x=4
240.x=254-4
240.x=250
x=250:240
x=25/24
vậy x=25/24
A. Âm vì \(\left(-\right)\left(+\right)=\left(-\right)\Leftarrow\left\{{}\begin{matrix}\left(-\right)\left(+\right)=\left(-\right)\\\left(-\right)\left(-\right)=\left(+\right)\end{matrix}\right.\)
(Theo tính chất phép nhân bạn nhé)
a/ A = 4 + 42 + 43 + ...... + 445 (1)
nhân 2 vế với 2 ta được
4A = 42 + 43 + 44 + ......... + 455 (2)
lấy (2) - (1) ta được'
4A - A = 455 - 4
3A = 455 - 4
A = ( 455 - 4 ) : 3
a) \(A=4+4^2+4^3+...+4^{50}\)
\(\Leftrightarrow4A=4^2+4^3+...+4^{51}\)
\(\Leftrightarrow4A-A=\left(4^2+4^3+...+4^{51}\right)-\left(4+4^2+4^3+...+4^{50}\right)\)
\(\Leftrightarrow3A=4^{51}-4\)
\(\Leftrightarrow A=\dfrac{4^{51}-4}{3}\)
(- 4) . (+21) . (- 25) . (- 2)
= (-4).(-25).(+21).(-2)
= 100.(+21).(-2)
= -4200
Đáp án: C