\(Q_{toa}=A=I^2Rt=2^2\cdot5\cdot1\cdot60=1200\left(J\right)\)

Chọn D

`S = 1/( 5 xx 9 ) + 1/( 9xx13 ) +.....+1/( 41xx45)`

   `= 1/4 xx ( 1/( 5 xx 9 ) + 1/( 9xx13 ) +.....+1/( 41xx45))`

   `= 1/4 xx ( 1/5 - 1/9 + 1/9 - 1/13 +....+1/41-1/45)`

   `= 1/4 xx ( 1/5 - 1/45 )`

   `= 2/45`

`4S = 1/(5xx9) + 1/(9xx13) + ... + 4/(41xx45)`

`4S = 1/5 - 1/9 + 1/9 - 1/13 + ... + 1/41 - 1/45`

`4S = 8/45`

`=> S = 2/45`

\(=3\cdot\left(\dfrac{10}{21}-\dfrac{3}{14}\right)\cdot\dfrac{14}{11}=3\cdot\dfrac{20-9}{42}\cdot\dfrac{14}{11}=3\cdot\dfrac{1}{3}=1\)

\(=3\times\dfrac{11}{42}:\dfrac{11}{14}\)

\(=\dfrac{11}{14}:\dfrac{11}{14}\)

\(=1\)

`= 3 xx 11/42:11/14`

`= 11/14:11/14`

`=1`

a) -10

b)6

c)-21

d)-25

tick nhé

a: =>x=-5x4:2=-10

b: =>48/x=8

hay x=6

c: \(\Leftrightarrow x=-14\cdot\dfrac{3}{2}=-21\)

d: \(\Leftrightarrow\dfrac{5}{x}=\dfrac{-1}{5}\)

hay x=-25

e: \(\Leftrightarrow x-2=12\)

hay x=14

f: \(\Leftrightarrow x+3=-5\)

hay x=-8

g: \(\Leftrightarrow x^2=100\)

hay \(x\in\left\{10;-10\right\}\)

h: \(\Leftrightarrow xy=-6\)

hay \(\left(x,y\right)\in\left\{\left(1;-6\right);\left(-6;1\right);\left(-1;6\right);\left(6;-1\right);\left(2;-3\right);\left(-3;2\right);\left(-2;3\right);\left(3;-2\right)\right\}\)

i: =>\(-4\left(x-5\right)=3x+6\)

=>-4x+20=3x+6

=>-7x=-14

hay x=2

k: =>3(x+1)=2(x-2)

=>3x+3=2x-4

hay x=-7

\(h.\dfrac{-2}{y}=\dfrac{x}{3}\left(đk:y\ne0\right)\)

\(\Leftrightarrow xy=-6\)

\(x=-\dfrac{6}{y}\left(với.y\ne0\right)\)

40: D

41: 

\(\Delta H=328,8kJ/mol\)

không bt em sai đâu không nhưng em ra  \(\Delta S=213,63+2.188,72-126,8-\dfrac{3}{2}.205,03=156,725J/mol.K\) ạ 

\(\dfrac{7}{2.9}+\dfrac{7}{9.16}+...+\dfrac{7}{86.93}=\dfrac{1}{2}-\dfrac{1}{9}+\dfrac{1}{9}-\dfrac{1}{16}+...+\dfrac{1}{86}-\dfrac{1}{93}=\dfrac{1}{2}-\dfrac{1}{93}=\dfrac{91}{186}=\dfrac{\overline{a1}}{\overline{bcd}}\)

\(=>a=9;b=1;c=8;d=6\)

Không có số nguyên tố

\(=>\)Chọn đáp án \(D\)

câu 6. 

C.8

câu 7.

B.\(\dfrac{1}{5}\)