\(a,\dfrac{1}{2}-\dfrac{1}{3}-\left(-\dfrac{5}{4}\right)=\dfrac{1}{2}-\dfrac{1}{3}+\dfrac{5}{4}=\dfrac{1\times6-1\times4+5\times3}{12}=\dfrac{6-4+15}{12}=\dfrac{17}{12}\\ b,\dfrac{5}{4}-\dfrac{1}{2}-\dfrac{7}{8}=\dfrac{5\times2-1\times4-7}{8}=\dfrac{10-4-7}{8}=-\dfrac{1}{8}\\ c,\dfrac{1}{5}-\dfrac{1}{2}+\dfrac{9}{10}=\dfrac{1\times2-1\times5+9}{10}=\dfrac{2-5+9}{10}=\dfrac{6}{10}=\dfrac{3}{5}\\ d,\dfrac{5}{4}-\dfrac{1}{3}+\dfrac{7}{6}=\dfrac{5\times3-1\times4+7\times2}{12}=\dfrac{15-4+14}{12}=\dfrac{25}{12}\)

`1/2+(-1/3)-(-5/4)`

`=1/2-1/3+5/4`

`=3/6-2/6+5/4`

`=1/6+5/4`

`=2/12+15/12`

`=17/12`

__

`5/4-1/2+(-7/8)`

`=5/4-1/2-7/8`

`=10/8-4/8-7/8`

`=6/8-7/8`

`=-1/8`

__

`1/5-1/2+9/10`

`=2/10-5/10+9/10`

`=-3/10+9/10`

`=6/10`

`=3/5`

__

`5/4-1/3+7/6`

`=15/12-4/12+14/12`

`=11/12+14/12`

`=25/12`

`#lv`

#\(N\)

`1, -3/7 +5/13 - 4/7 +-8/13 = (-3/7 + -4/7) + (5/13 --8/13) = -1+1=0`

`2, -5/14 - 2/14 + 1/8 + 1/8 = (-5/14 - 2/14) + (1/8 + 1/8) = -1/2 + 1/4 =-1/4`

`3, -5/22 -1 +3/2-6/22 = (-5/22 - 6/22) -1+3/2 = -1/2 - 1+3/2 = -3/2 + 3/2 = 0 `

`4, -1/2 + 1/4 + 2/8 -11/77 = -1/2+1/4 +1/4 -11/77 = -1/2 +(1/4+1/4)-1/7 =-1/2 + 1/2 - 1/7 =0-1/7 = -1/7`

`5, 2/5 + 5/4+(-2/5+5/4)-5/2 = 2/5+5/4+-2/5+5/4-5/2 = (2/5+-2/5)+(5/4+5/4)-5/2 = 0+5/2-5/2 = 5/2 - 5/2 = 0`

1: =-3/7-4/7+5/13+8/13

=-1+1=0

2: =-5/14-2/14+1/4

=-1/2+1/4

=-1/4

3: =-5/22-6/22+3/2-1

=-1/2-1+3/2

=0

4: =-4/8+2/8+2/8-1/7=-1/7

5: =2/5+5/4-2/5+5/4-5/2

=5/2-5/2

=0

\(\sqrt{2x+5}\) xác định khi \(2x+5\ge0\Rightarrow2x\ge-5\Rightarrow x\ge-\dfrac{5}{2}\)

\(\sqrt{2x+5}\le0\Leftrightarrow2x+5\le0\Leftrightarrow2x\le-5\Leftrightarrow x\ge\dfrac{-5}{2}\)

\(\Rightarrow\) Đáp án:   A

Chọn A

ĐKXĐ: \(2x-3\ge0\\ \Rightarrow2x\ge0+3\\ \Rightarrow2x\ge3\\ \Rightarrow x\ge\dfrac{3}{2}\left(A\right)\)

Chọn A

\(\sqrt{3-2x}\) xác định khi \(3-2x\ge0\Rightarrow2x\le3-0\Rightarrow2x\le3\Rightarrow x\le\dfrac{3}{2}\left(D\right)\)

câu d

\(\sqrt{3-2x}\) xác định khi: \(3-2x\ge0\)

Ta giải BPT:

\(3-2x\ge0\)

<=> \(-2x\ge-3\)

<=> \(-2x:\left(-2\right)\le-3:\left(-2\right)\)

<=> \(x\le\dfrac{3}{2}\)

= 2/3 + 1/3 . 7/18 : 5/12

= 2/3 + 7/54 : 5/12

= 2/3 + 14/45 

= 44/45

giúp tui ae

alo,ae cứu tui zới

Câu 7:

\(2Al_2O_3\underrightarrow{^{đpnc}}4Al+3O_2\\ m_{Al_2O_3}=95\%.1=0,95\left(tấn\right)\\ m_{Al\left(LT\right)}=\dfrac{108.0,95}{204}=\dfrac{171}{340}\left(tấn\right)\\ Vì:H=98\%\\ \Rightarrow m_{Al\left(TT\right)}=\dfrac{171}{340}.98\%=\dfrac{8379}{17000}\left(tấn\right)=\dfrac{8379}{17}\left(kg\right)\)