Bài 1:

\(a,x^2-y^2-2x+2y=\left(x-y\right)\left(x+y\right)-2\left(x-y\right)=\left(x-y\right)\left(x+y-2\right)\)

\(b,2x+2y-x^2-xy=2\left(x+y\right)-x\left(x+y\right)=\left(2-x\right)\left(x+y\right)\)

\(c,3a^2-6ab+3b^2-12c^2=3\left(a-b\right)^2-12c^2=3\left[\left(a-b\right)^2-4c^2\right]=3\left(a-b-2c\right)\left(a-b+2c\right)\)

\(d,x^2-25+y^2+2xy=\left(x-y\right)^2-25=\left(x-y-5\right)\left(x-y+5\right)\)

Bài 1:

\(e,a^2+2ab+b^2-ac-bc=\left(a+b\right)^2-c\left(a+b\right)=\left(a+b-c\right)\left(a+b\right)\)

\(f,x^2-2x-4y^2-4y=\left(x-1\right)^2-\left(2y+1\right)^2=\left(x-2y-2\right)\left(x+2y\right)\)

\(g,x^2y-x^3-9y+9x=x^2\left(y-x\right)-9\left(y-x\right)=\left(x-3\right)\left(x+3\right)\left(y-x\right)\)

\(h,x^2\left(x-1\right)+16\left(1-x\right)=\left(x-1\right)\left(x-4\right)\left(x+4\right)\)

Bài 2: 

1) \(4x^2-25+\left(2x+7\right)\left(5-2x\right)=\left(2x-5\right)\left(2x+5\right)-\left(2x+7\right)\left(2x-5\right)=\left(2x-5\right)\left(-2\right)\)

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

3) \(5x^2-5y^2-10x+10y=5\left(x-y\right)\left(x+y\right)-10\left(x-y\right)=5\left(x-y\right)\left(x+y-2\right)\)

4) \(x^2-xy+x-y=\left(x-y\right)\left(x+1\right)\)

chiều rộng bn tính là 140 nhân 2/7 = 40m                                                 a) diện tích là 140 nhân 40 = 5600m²                                                       đổi 5600m² = 0,5600 ha                                                                           b) 5600 gấp 100 số lần là                                                                         5600:100=56 lần                                                                                       trên cả thửa ruộng thu đc số thóc là                                          lấy 65 nhân 56= 3640 kg                                                                            đổi 3640=0,3640 tấn thóc                                                                   chúc bn học ngu nhầm học giỏi :)

Câu 2: 

uses crt;

var i,n,t:integer;

begin

clrscr;

n:=0;

t:=0;

repeat

n:=n+1;

t:=t+n;

until t>100;

writeln(t);

readln;

end.

C2:

var i,s: integer;

begin

while s<=100 do begin

s:=s+i;

i:=i+1;

end;

write(s);

readln

end.

pride

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Ultimately

2:

a: =>x-5=0 hoặc 2x-4=0

=>x=2 hoặc x=5

b: =>4x-4=2x-6x+12

=>4x-4=-4x+12

=>8x=16

=>x=2

c: =>9-x+x-6=3-x+12

=>15-x=3

=>x=12

d: =>-152-(3x+1)=54

=>3x+1=-152-54=-206

=>3x=-207

=>x=-69

Bài tập 1:

a) \(12x+2^4=4x-24\)

\(\Rightarrow12x+16=4x-24\)

\(\Rightarrow12x-4x=-24-16\)

\(\Rightarrow8x=-40\)

\(\Rightarrow x=\dfrac{-40}{8}=-5\)

b) \(6\left(4-x\right)-4\left(x-1\right)=2x+40\)

\(\Rightarrow24-6x-4x+4=2x+40\)

\(\Rightarrow28-10x=2x+40\)

\(\Rightarrow-10x-2x=40-28\)

\(\Rightarrow-12x=12\)

\(\Rightarrow x=-\dfrac{12}{12}=-1\)

c) \(12\left(2x+7\right)-9\left(3x-2\right)=72\)

\(\Rightarrow24x+84-27x+18=72\)

\(\Rightarrow24x-27x=72-84-18\)

\(\Rightarrow-3x=-30\)

\(\Rightarrow x=-\dfrac{30}{-3}=10\)

d) \(6\left(x-2\right)=20-4x\)

\(\Rightarrow6x-12=20-4x\)

\(\Rightarrow6x+4x=20+12\)

\(\Rightarrow10x=32\)

\(\Rightarrow x=\dfrac{32}{10}=\dfrac{16}{5}\)

\(\dfrac{130050}{425}=306\)

\(\dfrac{130050}{425}=306\)

\(\dfrac{130050}{425}=\dfrac{25x17x306}{25x17}=306\)

6B

10C

8A