Hãy nhập câu hỏi của bạn vào đây, nếu là tài khoản VIP, bạn sẽ được ưu tiên trả lời.
1) Ta có: \(\left(\dfrac{3}{4}\cdot\dfrac{5}{97}+\dfrac{1}{9}\cdot\dfrac{13}{47}\right)\cdot\left(\dfrac{1}{5}-\dfrac{7}{25}\cdot\dfrac{5}{7}\right)\)
\(=\left(\dfrac{3}{4}\cdot\dfrac{5}{97}+\dfrac{1}{9}\cdot\dfrac{13}{47}\right)\cdot\left(\dfrac{1}{5}-\dfrac{1}{5}\right)\)
=0
2) Ta có: \(\dfrac{8}{17}\cdot\dfrac{4}{15}+\dfrac{8}{17}\cdot\dfrac{22}{15}-\dfrac{8}{15}\cdot\dfrac{9}{17}\)
\(=\dfrac{8}{17}\left(\dfrac{4}{15}+\dfrac{22}{15}-\dfrac{9}{15}\right)\)
\(=\dfrac{8}{17}\cdot\dfrac{15}{15}=\dfrac{8}{17}\)
3) Ta có: \(\dfrac{2021}{2}\cdot\dfrac{1}{3}+\dfrac{4042}{4}\cdot\dfrac{1}{5}+\dfrac{6063}{3}\cdot\dfrac{22}{15}\)
\(=\dfrac{2021}{2}\left(\dfrac{1}{3}+\dfrac{1}{5}\right)+2021\cdot\dfrac{22}{15}\)
\(=\dfrac{2021}{2}\cdot\dfrac{8}{15}+\dfrac{2021}{2}\cdot\dfrac{44}{15}\)
\(=\dfrac{2021}{2}\cdot\dfrac{52}{15}\)
\(=\dfrac{52546}{15}\)
4) Ta có: \(\dfrac{4}{7}\cdot\dfrac{2}{13}+\dfrac{8}{13}:\dfrac{7}{4}+\dfrac{4}{7}:\dfrac{13}{2}+\dfrac{4}{7}\cdot\dfrac{1}{13}\)
\(=\dfrac{4}{7}\left(\dfrac{2}{13}+\dfrac{8}{13}+\dfrac{2}{13}+\dfrac{1}{13}\right)\)
\(=\dfrac{4}{7}\)
Áp dụng BĐT phụ \(a^2+b^2\ge\dfrac{1}{2}\left(a+b\right)^2\Leftrightarrow\left(a-b\right)^2\ge0\)
\(A\ge\dfrac{1}{2}\left(x+y+\dfrac{1}{x}+\dfrac{1}{y}\right)^2\ge\dfrac{1}{2}\left(x+y+\dfrac{4}{x+y}\right)^2=\dfrac{1}{2}\left(1+\dfrac{4}{1}\right)^2=\dfrac{25}{2}\)
Dấu "=" \(x=y=\dfrac{1}{2}\)
a) x* 1/5 - x* 2 * 2/15 = 4
x * 1/5 - x * 2 = 4 : 2/15
x * 15 - x * 2 = 30
x * ( 15 - 2 ) = 30
x * 13 = 30
x = 30 : 13
x = 30/13
b) ( x + x * 2 ) - 3 : 1/2 = 8
( x * 1 + x * 2 ) - 3 = 8 x 1/2
( x * 1 + x * 2 ) - 3 = 4
x * 1 + x * 2 = 4 + 3
x * 1 + x * 2 = 7
x * ( 1 + 2 ) = 7
x * 3 = 7
x = 7 : 3
x = 7/3
c)5 +( x * 1/2 - 4 ) = 15
x * 1/2 - 4 = 15 - 5
x * 1/2 - 4 = 10
x * 1/2 = 10 + 4
x * 1/2 = 14
x = 14 : 1/2
x = 7
a)x*1/5-x*2*2/15=4
x*1/5-x*4/15=4
x*1/5-4/15=4
x*(-1/15)=4
x=4:-1/15
x=-60
a) 13 - 2x = x- 2 b)2x-15+8x=7-2x+14 c)12-4y+3y=4y-10-8y
<=>13 + 2 = x+2x <=>2x +2x+8x =7+14+15 <=>12+10 =4y-8y+4y-3y
<=> 15 =3x <=>12x =36 <=> 22 =-3y
<=> x=5 <=>x=3 <=>y=-22/3
vậy S=[5] vậy S=[3] vậy S=[-22/3]
1: x=3/4-1/2=3/4-2/4=1/4
2: x-1/5=2/11
=>x=2/11+1/5=21/55
3: x-5/6=16/42-8/56
=>x-5/6=8/21-4/28=5/21
=>x=5/21+5/6=15/14
4: x/5=5/6-19/30
=>x/5=25/30-19/30=6/30=1/5
=>x=1
5: =>|x|=1/3+1/4=7/12
=>x=7/12 hoặc x=-7/12
6: x=-1/2+3/4
=>x=3/4-1/2=1/4
11: x-(-6/12)=9/48
=>x+1/2=3/16
=>x=3/16-1/2=-5/16
1)x= 1/4
2)x= 2/11+ 1/5
x= 21/55
3)x - 5/6 = 5/21
x = 5/21+5/6
x = 15/14
4)x/5 = 5/6 + -19/30
x:5 = 1/5
x = 1/5.5
x = 1
5) |x| - 1/4 = 6/18
|x| = 6/18 - 1/4
|x| =7/12
⇒x= 7/12 hoặc -7/12
6)x = -1/2 +3/4
x= 1/4
7) x/15 = 3/5 + -2/3
x:15 = -1/15
x = -1/15. 15
x = -1
8)11/8 + 13/6 = 85/x
85/24 = 85/x
⇒ x = 24
9) x - 7/8 = 13/12
x = 13/12 + 7/8
x = 47/24
10)x - -6/15 = 4/27
x = 4/27 + (-6/15)
x = -34/135
11) -(-6/12)+x = 9/48
x= 9/48 - 6/12
x = -5/16
12) x - 4/6 = 5/25 + -7/15
x -4/6 = -4/15
x = -4/15 + 4/6
x = 2/5
`@` `\text {Ans}`
`\downarrow`
`a)`
`x + 10 = 20`
`=> x = 20 -10`
`=> x = 10`
Vậy, `x = 10`
`b)`
`2 * x + 15 = 35`
`=> 2x = 35 - 15`
`=> 2x = 20`
`=> x = 20 \div 2`
`=> x = 10`
Vậy, `x = 10`
`c)`
`3 * ( x + 2 ) = 15`
`=> x + 2 = 15 \div 3`
`=> x + 2 = 5`
`=> x = 5 - 2`
`=> x = 3`
Vậy, `x = 3`
`d)`
`10 * x + 15 * 11 = 20 * 10`
`=> 10x + 165 = 200`
`=> 10x = 200 - 165`
`=> 10x = 35`
`=> x = 35 \div 10`
`=> x = 3,5`
Vậy,` x = 3,5`
`e)`
`4 * ( x + 2 ) = 3 * 4`
`=> x + 2 = 12 \div 4`
`=> x + 2 = 3`
`=> x = 3 - 2`
`=> x = 1`
Vậy,` x = 1`
`f)`
`33 x + 135 = 26 * 9`
`=> 33x + 135 = 234`
`=> 33x = 234 - 135`
`=> 33x = 99`
`=> x = 99 \div 33`
`=> x = 3`
Vậy, `x = 3`
`g)`
`2 * x + 15 + 16 + 17 = 100`
`=> 2x + 48 = 100`
`=> 2x = 100 - 48`
`=> 2x = 52`
`=> x = 52 \div 2`
`=> x =26`
`h)`
`2 * (x + 9 + 10 + 11) = 4 . 12 . 25`
`=> 2 * (x + 9 + 10 + 11) = 4*25*12`
`=> 2 * (x + 9 + 10 + 11) = 100*12`
`=> x + 9 + 10 + 11 = 100*12 \div 2`
`=> x + 30 = 600`
`=> x = 600 - 30`
`=> x = 570`
Vậy, `x = 570.`
a) \(x+10=20\Leftrightarrow x=10\)
b) \(2x+15=35\Leftrightarrow2x=20\Leftrightarrow x=10\)
c) \(3.\left(x+2\right)=15\Leftrightarrow x+2=5\Leftrightarrow x=3\)
d) \(10x+15.11=20.10\Leftrightarrow10x+165=200\Leftrightarrow10x=35\Leftrightarrow x=\dfrac{35}{10}=\dfrac{7}{2}\)
e) \(4.\left(x+2\right)=3.4\Leftrightarrow x+2=3\Leftrightarrow x=1\)
f) \(35x+135=26.9\Leftrightarrow35x=234-135\Leftrightarrow35x=99\Leftrightarrow x=\dfrac{99}{35}\)
g) \(2x+15+16+17=100\Leftrightarrow2x+48=100\Leftrightarrow2x=52\Leftrightarrow x=26\)
h) \(2.\left(x+9+10+11\right)=4.12.25\)
\(\Leftrightarrow x+30=2.12.25\)
\(\Leftrightarrow x=600-30\)
\(\Leftrightarrow x=570\)
\(-4+x=-4+7\)
\(\Rightarrow x=-4+7+4\)
\(\Rightarrow x=7\)
\(\left(-3\right)-\left(-5-x\right)=-15+\left(-6+15\right)\)
\(\Rightarrow x=-15-6+15+3-5\)
\(\Rightarrow x=-8\)
\(-\left(x+2\right)+2=\left(8-15\right)+15\)
\(\Rightarrow-x+2+2=-7+15\)
\(\Rightarrow-x=-7+15-2-2\)
\(\Rightarrow x=-4\)
\(4+\left(x-4\right)=-\left(11-2\right)+\left(11+4\right)\)
\(\Rightarrow4+x-4=-11+2+11+4\)
\(\Rightarrow x=-11+2+11+4-4+4\)
\(\Rightarrow x=6\)
a) -4 + x = -4 + 7 b) (-3) - (-5-x) = -15 + (-6+15)
-4 + x + 4 - 7 = 0 (-3) + 5 + x = -6
x - 7 = 0 2 + 6 = -x
x= 7 8 = -x
Vậy x= 7 x= -8 =) Vậy x= -8
c) -(x+2)+2=(8-15)+15 d) 4+(x-4)= -(11-2) + (11+4 )
-x - 2 + 2 = 8 4+x-4 = 6
-x = 8 x=6
x= -8 Vậy x=6
Vậy x= -8
Đặt t = x 2 – 4x ta được
t 2 + 8 t + 15 = t 2 + 3 t + 5 t + 15 = t(t + 3) + 5(t + 3) = (t + 5)(t + 3)
= ( x 2 – 4 x + 5 ) ( x 2 – 4 x + 3 ) = ( x 2 – 4 x + 5 ) ( x 2 – 3 x – x + 3 ) = ( x 2 – 4 x + 5 ) ( x ( x – 3 ) – ( x – 3 ) ) = ( x 2 – 4 x + 5 ) ( x – 1 ) ( x – 3 )
Vậy số cần điền là -3
Đáp số cần chọn là: A