Ta có: A = 1/1x2 + 1/2x3 + .... + 1/99x100

              = 1x(1/1x2 + 1/2x3 + ... + 1/99x100)

              = 1x(1 - 1/2 + 1/2 - 1/3 + ... + 1/99 - 1/100)

              = 1x(1-1/100)

              = 1 x 99/100

              = 99/100

Ta có: 99/100 < 1 vì tử số bé hơn mẫu số

=> A = 1/1x2+1/2x3+...+1/99x100 < 1

(ko bik cách trình bày)

Đặt \(S=\frac{3x+4}{2x+1}=\frac{2\left(3x+8\right)}{2\left(2x+1\right)}=\frac{6x+8}{2\left(2x+1\right)}=\frac{6x+3+5}{2\left(2x+1\right)}=\frac{3\left(2x+1\right)+5}{2\left(2x+1\right)}=\frac{3}{2}+\frac{5}{2x+1}\)

Xét\(2x+1< 0\Rightarrow\frac{5}{2\left(2x+1\right)}< 0\Rightarrow A>\frac{3}{2}\)

Xét \(2x+1< 0\)

Mà\(2x+1\in Z\)(vì \(x\in Z\))\(\Rightarrow2x+1\ge1\). Ta có:\(\frac{5}{2\left(2x+1\right)}< \frac{5}{2}\)

\(\Rightarrow A\ge\frac{3}{2}+\frac{5}{2}=\frac{8}{2}=4\)

\(\Rightarrow A=4\Leftrightarrow2x+1=1\Leftrightarrow2x=0\Leftrightarrow0\)

Vậy GTNN của A=4 khi x=0

M không phải là số chính phương vì M chia hết cho 10 nhưng ko chia hết cho 10²

1.He will get a cup of coffee.

2.The teacher will not punish that student.

3.If he doesn't eat breakfast he will be hungry.

4.We can reuse the bottles and cans.

5.We shouldn't throw rubbish on the street.

1.He will get a cup of coffee.

2.The teacher will not punish that student.

3.If he doesn't eat breakfast he will be hungry.

4.We can reuse the bottles and cans.

5.We shouldn't throw rubbish on the street.

\(\left(2\frac{4}{5}x-50\right)\div\frac{2}{3}=51\)

\(\frac{14}{5}x-50=51\times\frac{2}{3}\)

\(\frac{14}{5}x-50=34\)

\(\frac{14}{5}x=84\)

\(x=84\times\frac{5}{14}\)

\(x=30\)

\(a,\left(2\frac{4}{5}.x-50\right):\frac{2}{3}=51\)

    \(\left(\frac{14}{5}.x-50\right):\frac{2}{3}=51\)

   \(\frac{14}{5}.x-50=51\times\frac{2}{3}\)

   \(\frac{14}{5}.x-50=34\)

   \(\frac{14}{5}.x=34+50\)

   \(\frac{14}{5}.x=84\)

    \(x=84:\frac{14}{5}\)

   \(x=\frac{405}{14}\)

1.less => fewer

2.much => many

3.homeworks => homework

4.does it cost => it costs

5.an orange small => a small orange

1, I have less books in English than my friend.

\(\Rightarrow\)I have fewer books in English than my friend.

2,A lot of my friends play tennis, but not much of them play badminton.

\(\Rightarrow\) A lot of my friends play tennis, but not many of them play badminton.

3,Our teacher gives us much homeworks today.

\(\Rightarrow\) Our teacher gives us much homework today.

4,Do you know how much does it cost to fly to Australia?

\(\Rightarrow\) Do you know how much it cost to fly to Australia?

5,His sister often goes to school with an orange small bag.

\(\Rightarrow\) ,His sister often goes to school with a orange small bag.