`5,05ha=5,05*10000=50500m^2`

a)

`(2k-1)^2-9`

`=(2k-1-3)(2k-1+3)`

`=(2k-4)(2k+2)`

`=4(k-2)(k+1)`

có \(4⋮4=>4\left(k-2\right)\left(k+1\right)⋮4\) 

\(=>\left(2k-1\right)^2-9⋮4\)

b)

`4-(1+3k)^2`

`=(2-1-3k)(2+1+3k)`

`=(1-3k)(3+3k)`

`=3(1-3k)(1+k)`

có \(3⋮3=>3\left(1-3k\right)\left(1+k\right)⋮3\\ =>4-\left(1+3k\right)^2⋮3\)

`B=y^2-4y+5`

`=y^2-4y+4+1`

`=(y-2)^2+1`

với `y=12` ta có

`(12-2)^2+1=10^2+1=100+1=101`

1)

`(x+3)^3=x^3+3*x^2*3+3*x*3^2+3^3=x^3+9x^2+27x+27`

2)

`(1+x)^3=1^3+3*1^2*x+3*1*x^2+x^3=1+3x+3x^2+x^3`

3)

`(2-x)^3=2^3-3*2^2*x+3*2*x^2-x^3=8-12x+6x^2-x^3`

4)

`(x-3)^3=x^3-3*x^2*3+3*x*3^2-3^3=x^3-9x^2+27x-27`

`n_(Fe)=m/M=28/56=0,5(mol)`

`n_(H_2O)=m/M=36/18=2(mol)`

`(3x-4)^3=7+1^2019`

`(3x-4)^3=7+1`

`(3x-4)^3=8`

`(3x-4)^3=2^3`

`=>3x-4=2`

`3x=6`

`x=2`

`48xx(-1/4)^3+1/2`

`=48xx(-1/64)+1/2`

`=-3/4+1/2`

`=-3/4+2/4`

`=-1/4`

`-1/2xx4/7+15/4

`=-2/7+15/4`

`=-8/28+105/28`

`=97/28`

`

`2 6/31 -5/24+25/31-1 1/24+0,25`

`=68/31-5/24+25/31-25/24+1/4`

`=(68/31+25/31)+(-5/24-25/24)+1/4`

`=93/31-30/24+1/4`

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

`=3-4/4`

`=3-1`

`=2`