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phân tích từng số thành thừa số nguyên tố rồi tính .
VD: 1 :
4=22 ;;;6=2.3;;; 8=23 ;;;; 10 = 2.5 ;;;; 12 =22.3
=> BCNN(4;6;8;10;12)=23.3.5=`10
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a) (x.7 +8):5=10
x.7 +8= 10.5=50
x.7= 50-8=42
x= 42:7=6
b) 280: (7+3.x)=4
7+3.x= 4.280= 1120
3.x= 1120-7 =1113
x= 1113: 3= 371
c) (x.5) .19:13= 57
(x.5). 19= 57.13= 741
x.5= 741: 19= 39
x= 39:5 =7,8
d) 6.(28-8).x = 72
20.x= 72:6= 12
x= 12: 20= 0,6
e) 4. (36-4.x)= 3,2
36-4.x= 32:4= 0,8
-4.x= 0,8- 36= -35,2
x= -35,2 : -4 = 8,8
f) (x-15).3 :12= 6
(x-15).3 = 6. 12= 72
x-15= 72: 3= 24
x= 24+ 15= 39
g) (x:4+ 6) . 7 = 70
x:4+6= 70:7= 10
x:4= 10-6= 4
x= 4.4 = 16
h) (x:2+50) :5= 12
x:2+ 50= 12.5= 60
x:2= 60-50= 10
x= 10.2=20
l) 5.(7+3.x)= 140
7+3.x= 140:5 = 28
3.x= 28-7 =21
x= 21: 3= 7
k cho mình nhe
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\(\frac{7}{y}=\frac{1}{12}\)
\(=>\frac{7}{y}=\frac{7}{84}\)
\(=>y=84\)
\(\frac{9}{10}-y.\frac{3}{4}=\frac{2}{5}\)
\(y.\frac{3}{4}=\frac{9}{10}-\frac{2}{5}=\frac{1}{2}\)
\(y=\frac{1}{2}:\frac{3}{4}\)
\(y=\frac{1}{2}.\frac{4}{3}\)
\(y=\frac{2}{3}\)
\(\frac{5}{6}:\left[y+\frac{7}{9}\right]=\frac{3}{4}\)
\(y+\frac{7}{9}=\frac{5}{6}:\frac{3}{4}\)
\(y+\frac{7}{9}=\frac{5}{6}.\frac{4}{3}\)
\(y+\frac{7}{9}=\frac{10}{9}\)
\(y=\frac{10}{9}-\frac{7}{9}\)
\(y=\frac{3}{9}\)
\(y=\frac{1}{3}\)
1, 7/y=1/12
=>7.12=y
=>y=84
2, 9/10-y.3/4=2/5
=>y.3/4=9/10-2/5
=>y.3/4=1/2
=>y=1/2:3/4=2/3
3, 5/6[y+7/9]=3/4
=>y+7/9=5/6:3/4
=>y+7/9=10/9
=>y=10/9-7/9
=>y=1/3
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\(a.\)\(y-\frac{11}{3}=\frac{12}{5}\)
\(y=\frac{12}{5}+\frac{11}{3}\)
\(y=\frac{91}{15}\)
\(b.2-y=\frac{15}{6}\)
\(y=2-\frac{15}{6}\)
\(y=-\frac{1}{2}\)
\(c.y\times2\frac{2}{3}=\frac{4}{9}\)
\(y=\frac{4}{9}:2\frac{2}{3}\)
\(y=\frac{1}{6}\)
\(d.y:1\frac{2}{5}=\frac{21}{10}\)
\(y=\frac{21}{10}\times1\frac{2}{5}\)
\(y=\frac{147}{5}\)
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a)100-9:(372:3.y-1)-14=83
<=>100-9:(124y-1)-14=83
<=>86-9:(124y-1)=83
<=>9:(124y-1)=3
<=>124y-1=3
<=>124y=4
<=>y=\(\frac{1}{31}\approx0,3223\)
b)7260-120:24.y+924=528,3
<=>8184-5y=528,3
<=>5y=7655,7
<=>y=1531,14
c)2000-52:(615:3:y-15)-14=1984
<=>1986-52:(205:y-15)=1984
<=>52:(205:y-15)=2
<=>205:y-15=26
<=>205:y=41
<=>y=5
d)y+y.1/3+5/18=7/18
<=>4/3y=1/9
<=>y=1/12
e)13/15-(5/21+y)7/12=7/10
<=>7/12.(5/21+y)=1/6
<=>5/36+7/12y=1/6
<=>7/12y=1/36
<=>y=1/21\(\approx\)0,4762
h)y+2.y+3.y+...+10.y=49,5
<=>55y=49,5
<=>y=0,9
i)y.(1975/8.9+1885/9.10+1755/10.11+1579/11.12)=1/24
<=>7991,364899y=1/24
<=>y=33/6329161
tích nha mỏi tay quá
\(y-\frac{3}{4}=\frac{5}{12}:\frac{10}{3}\)
\(y-\frac{3}{4}=\frac{1}{8}\)
\(y=\frac{1}{8}+\frac{3}{4}\)
\(y=\frac{7}{8}\)
\(y-\frac{3}{4}=\frac{5}{12}\text{ : }\frac{10}{3}\)
\(y-\frac{3}{4}=\frac{1}{8}\)
\(y=\frac{1}{8}+\frac{3}{4}\)
\(y=\frac{7}{8}\)