Để \(\frac{\sqrt{x+1}}{\sqrt{x-2}}=\sqrt{\frac{x+1}{x-2}}\) là số nguyên thì \(\frac{x+1}{x-2}\) là số chính phương

Khi đó \(x+1⋮x-2\)

\(\Leftrightarrow x-2+3⋮x-2\)

\(\Leftrightarrow3⋮x-2\)

\(\Leftrightarrow x-2\in\left\{1;3;-1;-3\right\}\)

\(\Leftrightarrow x\in\left\{4;5;1;-1\right\}\)

Thay vào thử nha !

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câu 1: There is a tree 8m long. A carpenter wants to cut the tree into 16dm long logs. Knowing that, each time he saw 5 minutes, he saw a log, he rested for 3 more minutes. How long does it take for the carpenter to finish cutting the tree?

câu 2: Parents have 6 sons, each son has a younger sister. How many people are there in that family?

câu 3: Something that you have, when you share it with me, but when you share you won't have it?

II/ Choose the best answer.

1.     Mai hates eating fast food because it’s not good ……her health.

a.      on           b. for           c. at             d. in

2.     If you want to live long, you …… eat  much red meat.

a.      should              b. needn’t    c. have to    d. shouldn’t

3.      Don’t read in bed, ................ you’ll harm your eyes.

a.      or            b. and                   c. but           d. so