1c 2a 3b 4b 5d

tk:

6 They volunteer to help the victims whose houses were destroyed by a flood

7 Hue which attracts thousands of tourists every year was recognized by UNESCO as a World Heritage Site

8 He introduced me to his students most of whom were from abroad(tham khảo c8)

9 They gave me four bad tyres->tires one of which burst before I had driven four miles

10 The computer which they bought isn't powerful enough

11 Children enjoy reading the books whose coloured pictures

12. 1945 is the year when the revolution took place

13 Do you know the man about whom they are talking

6 They volunteer to help the victims whose houses were destroyed by a flood

7 Hue which attracts thousands of tourists every year was recognized by UNESCO as a World Heritage Site

8 He introduced me to his students most of whom were from abroad(tham khảo c8)

9 They gave me four bad tyres->tires one of which burst before I had driven four miles

10 The computer which they bought isn't powerful enough

11 Children enjoy reading the books whose coloured pictures

12. 1945 is the year when the revolution took place

13 Do you know the man about whom they are talking

Áp dụng bđt Cô-si cho 2 số dương, ta có

\(A=xyz\le\frac{\left(x+y\right)^2z}{4}=\frac{\left(x+y\right)\left(100-z\right)z}{4}\) (Vì\(x+y+z=100\)

\(A\le\frac{\left(x+y\right)3\left(100-z\right)2z}{24}\le\frac{\left(x+y\right)\left(300-3z+2z\right)^2}{24}=\frac{\left(x+y\right)\left(300-z\right)^2}{96}\)

Mà \(z\ge60\) \(x+y+z=100\Rightarrow x+y\le40\)

\(\Rightarrow A\le\frac{40\left(300-60\right)^2}{96}=24000\) 

Dấu '=' xảy ra khi \(z=60;x=y=40\)

dòng cuối mình viết lộn nha \(x=y=20\) chứ

vs lại bạn viết nhầm, đáng ra phải là \(A\le2400\)mới đúng

nhưng thôi mk cx cứ tk cho bn nhé

cảm ơn bạn nhiều

\(a,2x+1⋮x-2\)

\(=>2.\left(x-2\right)+5⋮x-2\)

Do \(2.\left(x-2\right)⋮x-2\)

\(=>5⋮x-2\)

\(=>x-2\inƯ\left(5\right)\)

Nên ta có bảng sau :

Vậy ...

\(b,3x+5⋮x\)

Do \(3x⋮x=>5⋮x\)

\(=>x\inƯ\left(5\right)\)

Nên ta có bảng sau :

Vậy ...

\(c,4x+1⋮2x+3\)

\(=>2.\left(2x+3\right)-5⋮2x+3\)

Do \(2.\left(2x+3\right)⋮2x+3\)

\(=>5⋮2x+3\)

\(=>2x+3\inƯ\left(5\right)\)

Nên ta có bảng sau :

Vậy ...

a) Ta có: 2x+1=2(x-2)+5

Để 2x+1 chia hết cho x-2 thì 2(x-2)+5 chia hết cho x-2

Vì 2(x-2) chia hết cho x-2

=> 5 chia hết cho x-2

Vì x thuộc Z => z-2 thuộc Ư (5)={-5;-1;1;5}

Nếu x-2=-5 => x=-3

Nếu x-2=-1 => x=1

Nếu x-2=1 => x=3

Nếu x-1=5 => x=6

b) Ta có 3x chia hết cho x với mọi x

=> Để 3x+5 chia hết cho x thì 5 chia hết cho x

Vì x thuộc Z => x thuộc Ư (5)={-5;-1;1;5}

c) Ta có: 4x+11=2(2x+3)+5

Để 4x+11 chia hết cho 2x+3 thì 2(2x+3)+5 chia hết cho 2x+3

Vì 2(2x+3) chia hết cho 2x+3 => 5 chia hết cho 2x+3

Vì x thuộc Z => 2x+3 thuộc Ư (5)={-5;-1;1;5}

Nếu 2x+3=-5 => 2x=-8 => x=-4

Nếu 2x+3=-1 => 2x=-4 => x=-2

Nếu 2x+3=1 => 2x=-2 => x=-1

Nếu 2x+3=5 => 2x=2 => x=1

K có ai lm câu d  giúp mk hả ???

Đặt 4+6+8+10+...+2012 là A

Ta có: số số hạng A là:(2012-4)/2+1=1005

          tổng A là:(2012+4).1005/2=1013040

=1013040.\(\frac{1}{1000}\) .(\(\frac{1}{2}+\frac{3}{4}+\frac{5}{6}\))

=1013,04.(\(\frac{6}{12}+\frac{9}{12}+\frac{10}{12}\))

=1013,04.\(\frac{25}{12}\)

=2110,5

Hãy cho anh

thank you very much!!!!

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