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( x + 1 ) + ( x + 2 ) + ( x + 3 ) + ( x + 4 ) + ( x + 5 ) = 65
( x + x + x + x + x ) + ( 1 + 2 + 3 + 4 = 5 ) = 65
x * 5 +15 = 65
x * 5 = 65 - 15
x * 5 = 50
x = 50 : 5
x = 10
( X + 1 ) + ( X + 2 ) + ( X + 3 ) + ( X + 4 ) + ( X + 5 ) = 65
X x 5 + ( 1 + 2 + 3 + 4 + 5 ) = 65
X x 5 + 15 = 65
X x 5 = 65 - 15
X x 5 = 50
X = 50 : 5
X = 10
![](https://rs.olm.vn/images/avt/0.png?1311)
(x+1) + ( x+2) + (x+3) + (x+4) + ( x+5)= 65
(x+x+x+x+x)+(1+2+3+4+5)=65
x*5+15=65
x*5=65-15
x*5=50
x=10
<=>(x+x+x+x+x)+(1+2+3+4+5)=65
=>5x+15=65
=>5x=65-15
=>5x=50
=>x=50:5
=>x=10
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\(a.\left(17x-25\right)\div8+65=81\)
\(\left(17x-25\right):8=81-65\)
\(\left(17x-25\right):8=16\)
\(17x-25=16\times8\)
\(17x-25=128\)
\(17x=128+25\)
\(17x=153\)
\(x=153\div17\)
\(x=9.\)
\(b.720\div\left[41-\left(2x-5\right)\right]=8\times5\)
\(720\div\left[41-\left(2x-5\right)\right]=40\)
\(\left[41-\left(2x-5\right)\right]=720\div40\)
\(\left[41-\left(2x-5\right)\right]=18\)
\(2x-5=41-18\)
\(2x-5=23\)
\(2x=23+5\)
\(2x=28\)
\(x=28\div2\)
\(x=14.\)
\(c.231-\left(x-6\right)=1339\div13\)
\(231-\left(x-6\right)=103\)
\(x-6=231-103\)
\(x-6=128\)
\(x=128+6\)
\(x=134.\)
a) => ( 17x-25 ) : 8 = 16 => ( 17x -25 ) = 128 => 17x = 103 = >x = 103/7
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420 + 65 . 4 = ( x + 175 ) : 5 + 30
420 + 260 = ( x + 175 ) : 5 + 30
680 = ( x + 175 ) : 5 + 30
680 - 30 = ( x + 175 ) : 5
650 = ( x + 175 ) : 5
650 . 5 = x + 175
3250 = x + 175
x = 3250 - 175
x = 3075
420+260=(x+175):5+30
680=(x+175):5+30
680-30=(x+175):5
650x5=x+175
3250=x+175
X=3250-175
X=3075
![](https://rs.olm.vn/images/avt/0.png?1311)
a. 420+65×4=(x+175):5+30
(x+175):5+30=420+260
(x+175):5+30=680
(x+175):5=650
x+175=3250
x=3075
b.(32×15):2=(x+70):14-40
(x+70):14-40=480:2
(x+70):14-40=240
(x+70):14=280
x+70=3920
x=3850
~~~~~~~~~~~ai đi ngang qua nhớ để lại k ~~~~~~~~~~~~~
~~~~~~~~~~~~ Chúc bạn sớm kiếm được nhiều điểm hỏi đáp ~~~~~~~~~~~~~~~~~~~
~~~~~~~~~~~ Và chúc các bạn trả lời câu hỏi này kiếm được nhiều k hơn ~~~~~~~~~~~~
mik khỏi chép lại đề nha
a) 680 = (x + 175) : 5 + 30
(x + 175) : 5 = 680 - 30
(x + 175) : 5 = 650
x + 175 = 650 x 5
x + 175 = 3250
x = 3250 - 175
x = 3075
b) 240 = (x + 70) : 14 - 40
(x + 70) : 14 = 240 + 40
(x + 70) : 14 = 280
x + 70 = 280 x 14
x + 70 = 3920
x = 3920 - 70
x = 3850
tk mik nha b
x + 175 = 130
x =
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Bài 1:
\(A=\frac{1}{\left(1+2\right)}+\frac{1}{\left(1+2+3\right)}+\frac{1}{\left(1+2+3+4\right)}\)\(+\frac{1}{\left(1+2+3+4+5\right)}+...+\)\(\frac{1}{\left(1+2+3+...+10\right)}\)
\(A=\frac{1}{3}+\frac{1}{6}+....+\frac{1}{55}\)
\(A=2\left(\frac{1}{6}+\frac{1}{12}+....+\frac{1}{110}\right)\)
\(A=2\left(\frac{1}{2.3}+\frac{1}{3.4}+...+\frac{1}{10.11}\right)\)
\(A=2\left(\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+....+\frac{1}{10}-\frac{1}{11}\right)\)
\(A=2.\left(\frac{1}{2}-\frac{1}{11}\right)\)
\(A=\frac{9}{11}\)
Bài 2 :
2) Tử số = 11 x 13 x 15 + 3 x 3 x 3 x 11 x 13 x 15 + 5 x 5 x 5 x 11 x 13 x 15 + 9 x 9 x 9 x 11 x 13 x 15
= (1 + 3 x 3 x 3 + 5 x 5 x 5 + 9 x 9 x9) x 11 x 13 x 15 = (1+27+125+ 729) x 11 x 13 x 15
Mẫu số = 11 x 13 x 17 + 3 x 3 x 3 x 13 x 15 x 19 + 5 x 5 x 5 x 13 x 15 x 17 + 9 x 9 x 9 x 13 x 15 x 17 lớn hơn 11 x 13 x 15 + 3 x 3 x 3 x 13 x 15 x 17 + 5 x 5 x 5 x 13 x 15 x 17 + 9 x 9 x 9 x 13 x 15 x 17
= (1 + 3 x 3 x 3 + 5 x 5 x 5 + 9 x 9 x9) 13 x 15 x 17 = (1+27+125+729) x 13 x 15 x 17
\(\Rightarrow A< \frac{\left(1+27+125+729\right)\times11\times13\times15}{\left(1+27+125+729\right)\times13\times15\times17}\)
\(=\frac{11}{17}\)
\(=\frac{1111}{1717}=B\)
Vậy \(A=B\)
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35 . 34 + 35 . 38 + 65 . 75 + 65 . 45 + 35 . 34 =
= 35 . 34 + 35 . 38 + 35 . 34 + 65 . 75 + 65 . 45
= 35 . ( 34 + 38 + 34 ) + 65 . ( 75 + 45 )
= 35 . 110 + 65 . 110
= 110 . ( 35 + 65 )
= 110 . 100
= 11000
Hok tốt!!!!!!!!!!!!!
a) Tính bằng cách hợp lí nhất :
35 . 34 + 35 . 38 + 65 . 75 + 65 . 45 + 35 . 34
= 35 . 34 + 35 . 38 + 35 . 34 + 65 . 75 + 65 . 45
= 35 . ( 34 + 38 + 34 ) + 65 . ( 75 + 45 )
= 35 . 106 + 65 . 120
= 3710 + 7800
= 11510
3 . 25 . 8 + 4 . 37 . 6 + 2 . 38 . 12
= 3 . 8 . 25 + 4 . 6 . 37 + 2 . 12 . 38
= 24 . 25 + 24 . 37 + 24 . 38
= 24 . ( 25 + 37 + 38 )
= 24 . 100
= 2400
b) Tìm số tự nhiên x, biết :
( x - 5 ) ( x + 7 ) = 0
\(\Rightarrow\orbr{\begin{cases}x-5=0\\x+7=0\end{cases}\Rightarrow\orbr{\begin{cases}x=5\\x=-7\end{cases}}}.\)
Vậy .......
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= ( 0 ) * ( 4/31 + 5/65 + 7/29)
= 0
Vì số nào nhân với 0 cũng bằng 0
Nhớ k cho mik với nha
\(=\left(\frac{1}{6}-\frac{1}{6}\right)\cdot\left(\frac{4}{31}+\frac{5}{65}+\frac{7}{29}\right)\)
\(=0\cdot\left(\frac{4}{31}+\frac{5}{65}+\frac{7}{29}\right)\)
\(=0.\)
\(2\times\left(x\times4\right)+5=65\\ 2\times x\times4=65-5\\ x\times8=60\\ x=\dfrac{60}{8}=\dfrac{15}{2}\)
2 x ( X x 4 ) + 5 = 65
2 x ( X x 4 ) = 65 - 5
2 x ( X x 4 ) = 60
X x 4 = 60 : 2
X x 4 = 30
X = 30 : 4
X = 7,5
Vậy X = 7,5