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Tạm thời chức năng bị khoá nên hơi lâu em đừng hỏi linh tinh nữa nấm
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a: Khi m=3 thì (1): x^2-6x+4=0
=>x^2-6x+9-5=0
=>(x-3)^2=5
=>\(x=3\pm\sqrt{5}\)
![](https://rs.olm.vn/images/avt/0.png?1311)
81a.
$A=x(x+2)(x+3)(x+5)+9$
$=x(x+5)(x+2)(x+3)+9=(x^2+5x)(x^2+5x+6)+9$
$=(x^2+5x)^2+6(x^2+5x)+9$
$=(x^2+5x+3)^2$
81b.
$B=(x+2)(x+4)(x+6)(x+8)+16=(x+2)(x+8)(x+4)(x+6)+16$
$=(x^2+10x+16)(x^2+10x+24)+16$
$=a(a+8)+16$ (đặt $x^2+10x+16=a$)
$=a^2+8a+16=(a+4)^2=(x^2+10x+16+4)^2$
$=(x^2+10x+20)^2$
81c.
$C=(x^2+x)^2+9x^2+9x+14=(x^2+x)^2+9(x^2+x)+14$
$=a^2+9a+14$ (đặt $x^2+x=a$)
$=(a^2+7a)+(2a+14)=a(a+7)+2(a+7)$
$=(a+2)(a+7)=(x^2+x+2)(x^2+x+7)$
81d.
$D=x^2+2xy+y^2+2x+2y-15$
$=(x^2+2xy+y^2)+(2x+2y)-15=(x+y)^2+2(x+y)-15$
$=a^2+2a-15$ (đặt $x+y=a$)
$=(a^2-3a)+(5a-15)=a(a-3)+5(a-3)=(a-3)(a+5)$
$=(x+y-3)(x+y+5)$
81e.
$E=x^2-2xy+y^2+2x-2y-3=(x^2-2xy+y^2)+(2x-2y)-3$
$=(x-y)^2+2(x-y)-3=a^2+2a-3$ (đặt $x-y=a$)
$=(a^2-a)+(3a-3)=a(a-1)+3(a-1)=(a+3)(a-1)$
$=(x-y+3)(x-y-1)$
81g.
$G=(x^2+x)^2+5y(x^2+x)+6y^2$
$=(x^2+x)^2+2y(x^2+x)+3y(x^2+x)+6y^2$
$=(x^2+x)(x^2+x+2y)+3y(x^2+x+2y)$
$=(x^2+x+2y)(x^2+x+3y)$
81h.
$H=(x^2-x+1)(x^2+3x+1)+4x^2$
$=(a-x)(a+3x)+4x^2$ (đặt $x^2+1=a$)
$=a^2+2ax+x^2=(a+x)^2=(x^2+1+x)^2$
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Chu vi sân hình chữ nhật: \(\left(12+4\right).2=32\left(m\right)\)
Số tiền cần để làm rào: \(32.240000=7680000\left(đồng\right)\left(A\right)\)
![](https://rs.olm.vn/images/avt/0.png?1311)
câu 17
FE+H2SO4->FeSO4+H2
0,4----0,4---------0,4--------0,4
n Fe=0,4 mol
=>m H2SO4=0,4.98=39,2g
=>VH2=0,4.22,4=8,96l
CuO+H2-to>Cu+H2O
0,4----0,4
=>m Cu=0,4.64=25,6g
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D
2 You should say you are sorry
3 He ought ask his teacher about it
4 You should start having lessons
5 She ought not to watch TV late
6 You should get some exercise
E
1 can
2 could
3 ought
4 can
5 should
6 couldn't
7 can't
8 ought to
9 can
10 can
F
1 - D
2 - C
3 - B
4 - E
5 - A
2 You should say you are sorry
3 He ought ask his teacher about it
4 You should start having lessons
5 She ought not to watch TV late
6 You should get some exercise
2. Bill got most of them right
3. she got some of them right
4. he got most of them right
5. he got all of them right
6. he got none right
*Sxl
2. Bill got most of them right.
3. She got some of them right.
4. He got most of them right.
5. He got all of them right.
6. He got none right.