cần j tận căn v tr

giống tui vừa nãy cx ra x=1 :V

xuống dưới đê

\(a,\dfrac{38\times29+15}{38\times30-23}\\ =\dfrac{38\times29+15}{38\times\left(29+1\right)-23}\\ =\dfrac{38\times19+15}{38\times29+38-23}\\ =\dfrac{38\times19+15}{38\times19+15}\\ =1\\ b,\dfrac{17}{24}\times\dfrac{37}{12}-\dfrac{17}{24}\times\dfrac{1}{12}\\ =\dfrac{17}{24}\times\left(\dfrac{37}{12}-\dfrac{1}{12}\right)\\ =\dfrac{17}{24}\times\dfrac{36}{12}\\ =\dfrac{17}{24}\times3\\ =\dfrac{17}{8}\)

`(3x-5)(x+1)-(3x-1)(x-1)=x-4`

`<=>(3x^2 -5x+3x-5)-(3x^2 -x-3x+1)-x+4=0`

`<=>(3x^2 -2x-5)-(3x^2 -4x+1)-x+4=0`

`<=>3x^2 -2x-5-3x^2 +4x-1-x+4=0`

`<=>x-2=0`

`<=>x=2`

Vậy `S={2}`

`P=-2x^2 +6x+9`

`=-2(x^2 -3x-9/2)`

`=-2[(x^2 - 2. 3/2 .x + 9/4) - 27/4]`

`=-2[(x -3/2)^2 - 27/4]`

`=-2(x -3/2)^2 + 27/2 <= 27/2`

Dấu "=" xảy ra `<=>x -3/2 = 0 <=> x=3/2`

Vậy `P_(max)= 27/2 <=> x= 3/2`

\(\dfrac{1}{2}ha=\dfrac{1}{2}.10000=5000\\ \dfrac{1}{100}ha=\dfrac{1}{100}.10000=100m^2\\ \dfrac{1}{10}km^2=\dfrac{1}{10}.100=10ha\\ \dfrac{3}{4}km^2=\dfrac{3}{4}.100=75ha\)

`a,18xx28+36xx36`

`=18xx28+18xx2xx36`

`=18xx28+18xx72`

`=18xx(28+72)`

`=18xx100`

`=1800`

`b,24000-36xx75-36xx25`

`=24000-(36xx75+36xx25)`

`=24000-36xx(75+25)`

`=24000-36xx100`

`=24000-3600`

`=20400`

`c,2045-382+955-618`

`=(2045+955)-(382+618)`

`=3000-1000`

`=2000`