Don't spend too many of your time in the arcade.

many => much

Chắc vậy 

Why are you so late? - I couldn't find my keys.

Every day, Hoa gets up early to take morning exercises.

Hello.Is this Long? - Yes, it is

\(D=\frac{1}{2}+\frac{1}{2.3}+\frac{1}{3.4}+...\frac{1}{99.100}\)

\(D=\frac{1}{1}-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}...\frac{1}{99}-\frac{1}{100}\)

\(D=\frac{1}{1}-\frac{1}{100}\)

\(D=\frac{99}{100}\)

Vậy tổng D bằng \(\frac{99}{100}\)

Đặt \(\frac{x}{2}=\frac{y}{5}\)=k ta có: x=2k; y=5k

\(\Rightarrow\)2k.5k=40

\(\Rightarrow\)10k\(^2\)=40

\(\Rightarrow\)k\(^2\)=40:10

\(\Rightarrow\)k\(^2\)=4

=>k=+-2

Với k=2=>x=4;y=10

Với k=-2=>x=-4;y=-10

Vậy (x;y)=(4;10)=(-4;-10)

mk nek

Hi, mk nek