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a) X = 15
b) X = 4
c ) X= 23
d) X= 11
( Chỉ là ý kiến riêng thôi nhé, nhận gạch đá )
a) \(\frac{6+x}{33}=\frac{7}{11}\)
=> (6 + x). 11 = 33.7
=> 66 + 11x = 231
=> 11x = 231 - 66
=> 11x = 165
=> x = 165 : 11
=> x = 15
b) 15/26 + x/13 = 46/52
=> x/13 = 23/26 - 15/26
=> x/13 = 4/13
=> x = 4
c) 121/27 x 54/11 < x < 100/21 : 25/126
=> 22 < x < 24
=> x = 23 (vì x là số tự nhiên)
d) 1 < 11/x < 12
=> 11/x \(\in\){2; 3; 4 ; ...; 11}
=> x \(\in\) {11/2; 11/3; ...; 1}
Vì x là số tự nhiên => x = 1
\(\frac{121}{27}\times\frac{54}{11}< x< \frac{100}{21}\times\frac{126}{25}\)
\(22< x< 24\)
\(\left(a\right)\frac{34-x}{30}=\frac{5}{6}\)
\(\frac{34-x}{30}=\frac{25}{30}\)
34 - x = 25
x = 34 - 25 = 9
\(\left(b\right)\frac{x+13}{34}=\frac{12}{17}\)
\(\frac{x+13}{34}=\frac{24}{34}\)
x + 13 = 24
x = 24 - 13 = 11
\(\left(c\right)\left(x+\frac{1}{3}\right)+\left(x+\frac{1}{9}\right)+\left(x+\frac{1}{27}\right)+\left(x+\frac{1}{81}\right)=\frac{56}{81}\)
\(4x+\frac{1}{3}+\frac{1}{9}+\frac{1}{27}+\frac{1}{81}=\frac{56}{81}\)
Đặt \(A=\frac{1}{3}+\frac{1}{9}+\frac{1}{27}+\frac{1}{81}\)
Ta có : \(3A=1+\frac{1}{3}+\frac{1}{9}+\frac{1}{27}\)
\(3A-A=1+\frac{1}{3}+\frac{1}{9}+\frac{1}{27}-\frac{1}{3}-\frac{1}{9}-\frac{1}{27}-\frac{1}{81}\)
\(2A=1-\frac{1}{81}=\frac{80}{81}\)
\(A=\frac{80}{81}\div2=\frac{40}{81}\)
\(\Rightarrow4x+\frac{40}{81}=\frac{56}{81}\)
\(4x=\frac{56}{81}-\frac{40}{81}\)
\(4x=\frac{16}{81}\)
\(x=\frac{16}{81}\div4=\frac{4}{81}\)
Bài 1:
Câu D
Bài 2
0,2999<0,29999;0,299999;0,2999999<3/10
=>3 giá trị của x=(0,29999;0,299999;0,2999999)
a,D
b,\(\frac{3}{10}=0,3\)
suy ra 0,2999<x<0,3 suy ra x=0,29991,x=0,29992,x=0,29993
bài 6 \(\frac{2}{2\times4}+\frac{2}{4\times6}+\frac{2}{6\times8}+\ldots+\frac{2}{80\times82}+\frac{2}{82\times84}\)
= \(\frac12-\frac14+\frac14-\frac16+\frac16-\cdots+\frac{1}{80}-\frac{1}{82}+\frac{1}{82}-\frac{1}{84}\)
= \(\frac12-\left(\frac14-\frac14\right)-\left(\frac16-\frac16\right)-\cdots-\left(\frac{1}{82}-\frac{1}{82}\right)-\frac{1}{84}\)
=\(\frac12-0-0-\frac{1}{84}\)
=\(\frac12\) - \(\frac{1}{84}\)
=\(\frac{42}{84}-\frac{1}{84}\)
=\(\frac{41}{84}\)
Bài 7
a)\(\frac{19}{4}=4\frac34\)
b)\(\frac{27}{5}=5\frac25\)
c)\(\frac{56}{8}=7\frac08\)
a; (5142 - 17 x 8 + 242 : 11) x (27 - 3 x 9)
= (5142 - 17 x 8 + 242 : 11) x (27 - 27)
= (5142 - 17 x 8 + 242 : 11) x 0
= 0
b;
(1 + \(\dfrac{1}{2}\)) \(\times\) (1 + \(\dfrac{1}{3}\)) \(\times\) ( 1 + \(\dfrac{1}{4}\)) \(\times\) ... \(\times\) (1 + \(\dfrac{1}{2010}\)) \(\times\)(1 + \(\dfrac{1}{2011}\))
= \(\dfrac{2+1}{2}\) \(\times\) \(\dfrac{3+1}{3}\) \(\times\) \(\dfrac{4+1}{4}\)\(\times\) ... \(\times\) \(\dfrac{2010+1}{2010}\)\(\times\) \(\dfrac{2011+1}{2011}\)
= \(\dfrac{3}{2}\)\(\times\)\(\dfrac{4}{3}\)\(\times\)\(\dfrac{5}{4}\)\(\times\)...\(\times\)\(\dfrac{2011}{2010}\)\(\times\)\(\dfrac{2012}{2011}\)
= \(\dfrac{2012}{2}\)
= 1006
a) \(x\in\left\{20;21;22;...;25;26\right\}\)
b) \(x\in\left\{1;2;3;4;...;26;27\right\}\)
c) \(x\in\left\{47;48\right\}\)
\(A=\left\{20;21;22;23;24;25;26\right\}\)
\(B=\left\{1;2;3;4;5;6;7;8;9;10;11;12;13;14;15;...;27\right\}\)
\(C=\left\{47;48\right\}\)
\(A=\left\{20,21,22,23,24,25,26\right\}\)
\(B=\left\{1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27\right\}\)
\(C=\left\{47,48\right\}\)
K nha
A={18;19;20;21;22;23;24;25;26}
B={1;2;3;4;5;6;7;...;25;26;27}
C={47;48}
A = {20 ;21 ;22 ;23 , 24 ;25 ;26 }
B= { 1; 2 ;3 ; 4 ; 5 ; 6 ; 7 ; 8 ;9;10;11;12;13;14;15;16;17;18;19;20;21;22;23;24;25;26;27 }
C = {47;48 }
a, A={20;21;22;23;24;25;26}
b, B={1;2;3;4;5;6;...;25;26}
c, C={47;48}
A =20,21,22,....,25,26
B =1,2,3,....,24,25,26
C =47,48
hok tot