\(a,=5x-10+2x+6=7x-4\\ b,=x^2+2x+1-x^2+3x+10=5x+11\\ c,=x^2-49-x^2+1=-48\\ d,\text{Đề có sai ko vậy?}\)

1: Ta có: \(x^2-2x+5-\left(x-7\right)\left(x+2\right)\)

\(=x^2-2x+5-x^2-2x+7x-14\)

\(=3x-9\)

2: Ta có: \(-5x\left(x-5\right)+\left(x-3\right)\left(x^2-7\right)\)

\(=-5x^2+25x+x^3-7x-3x^2+21\)

\(=x^3-8x^2+18x+21\)

3: Ta có: \(x\left(x^2-x-2\right)-\left(x+5\right)\left(x-1\right)\)

\(=x^3-x^2-2x-x^2-4x+5\)

\(=x^3-2x^2-6x+5\)

=4x^2-4x+1+x^2+6x+9-5x^2+245

=2x+255

a: \(M=\dfrac{x^2\left(x-2\right)}{x-2}+\dfrac{\left(x+1\right)\left(x^2-x+1\right)}{x^2-x+1}=x^2+x+1\)

b: Để M=7 thì (x+3)(x-2)=0

=>x=-3(nhận) hoặc x=2(loại)

Vậy: x=-3

`a)(2x-1)^2+(x+3)^2-5(x-7)(x+7)`

`=4x^2-4x+1+x^2+6x+9-5(x^2-49)`

`=5x^2-5x^2-4x+6x+1+9+245`

`=2x+255`

`b)(x-2)(x^2+2x+4)-(25+x^3)`

`=x^3-8-x^3-25=-33`

Lời giải:

a. 

$(2x-1)^2+(x+3)^2-5(x-7)(x+7)$

$=4x^2-4x+1+(x^2+6x+9)-5(x^2-49)$

$=5x^2+2x+10-(5x^2-245)=2x+255$

b.

$(x-2)(x^2+2x+4)-(25+x^3)=(x^3-2^3)-(25+x^3)$

$=-8-25=-33$

a: Đặt A=3(5x-2)-|x-5|

TH1: x>=5

=>x-5>=0

A=3(5x-2)-|x-5|

=15x-6-(x-5)

=15x-6-x+5

=14x-1

TH2: x<5

=>x-5<0

A=3(5x-2)-|x-5|

=15x-6-(5-x)

=15x-6-5+x

=16x-11

b: Đặt B=|2x+3|+2x+7

TH1: x>=-3/2

=>2x+3>=0

B=|2x+3|+2x+7

=2x+3+2x+7

=4x+10

TH2: x<-3/2

=>2x+3<0

B=|2x+3|+2x+7

=-2x-3+2x+7

=4

c: đặt C=3x-1+|1-3x|

=3x-1+|3x-1|

TH1: x>=1/3

=>3x-1>=0

C=3x-1+|3x-1|

=3x-1+3x-1

=6x-2

TH2: x<1/3

=>3x-1<0

C=3x-1+|3x-1|

=3x-1+1-3x

=0

d: Đặt D=3(x-1)-2|x+3|

TH1: x>=-3

=>x+3>=0

D=3(x-1)-2|x+3|

=3(x-1)-2(x+3)

=3x-3-2x-6

=x-9

TH2: x<-3

=>x+3<0

D=3(x-1)-2|x+3|

=3x-3-2(-x-3)

=3x-3+2x+6

=5x+3

\(\left(2x-1\right)\left(1+2x\right)-3\left(x-3\right)^2-\left(2+x\right)^2\)

\(=\left(2x-1\right)\left(2x+1\right)-3\left(x^2-6x+9\right)-\left(4+4x+x^2\right)\)

\(=4x^2-1-3x^2+18x-27-4-4x-x^2\)

\(=14x-32\)

Phần b ,c giải phương trình??

\(\left(2x-3\right)^2+\left(3-x\right)^2+2\left(3-x\right)\left(2x-3\right)=5\)

\(\Leftrightarrow\left(2x-3\right)\left(2x-3+2\left(3-x\right)\right)+\left(3-x\right)^2=5\)

\(\Leftrightarrow\left(2x-3\right)\left(2x-3+6-2x\right)+\left(3-x\right)^2=5\)

\(\Leftrightarrow3\left(2x-3\right)+9-6x+x^2=5\)

\(\Leftrightarrow6x-9+9-6x+x^2=5\)

\(\Leftrightarrow x^2=5\)

\(\Leftrightarrow x=\pm\sqrt{5}\)

\(\left(x+5\right)\left(5-x\right)+\left(2x-1\right)^2-\left(3x-1\right)\left(x+2\right)-7=0\)

\(\Leftrightarrow\left(5-x\right)\left(5-x\right)+4x^2-4x+1-\left(3x^2+6x-x-2\right)-7=0\)

\(\Leftrightarrow25-x^2+4x^2-4x+1-3x^2-6x+x+2-7=0\)

\(\Leftrightarrow21-9x=0\)

​\(\Leftrightarrow9x=21\)​

\(\Leftrightarrow x=3\)