Vì n là số tự nhiên có 2 chữ số thì 10 lớn hơn hoặc bằng n bé hoặc bằng 99

=>21 lớn hơn hoặc bằng 2n+1 bé hơn hoặc bằng 199

Vì 2n+1 là số chính phương

=>2n+1={16;25;36;499;64;81;100;121;169}

=>n={12;24;40;60;84}

=>3n+1={37;73;121;181;253}

Mà 3n+1 là số chính phương

=>3n+1=121

=>n=40

Chúc bạn học tốt

Everyone has an ideal living place.First,my ideal living place will has fresh air and clean water so good for healthy and save a lots of money.Second,my house will be near the beatiful beach .And my neighbors are very friendly and on the roof has a swimming pool ,my family can will be can swim.My house will be near market and my school.I hope my house will can help me save money . What about you?

1.They must clean and tidy their school.

->They must keep their school clean and tidy

2.Some vistors to Britain get depressed by the weather.

->Some visitors to Britain find the weather get depressing

3.Nam has no problems in making friends.

->Nam finds it is easy to make friends

4.He found that it was difficult to tell them the truth.

->He found it was difficult to tell the truth

5.English pronunciation confuses us.

->We find English pronunciation confusing

Chúc Bạn Học Tốt

1106 chắc với bạn luôn đấy 

cho ****

1. It's about 2km from my house to the movie theater (How far)

=>How far is it from your house to the movie theatre ?

2.My father is an engineer (What)

=>What does your father do ?

3.Viet doesn't want to go to my house because he has too many assignments. (Why)

=>Why doesn't Viet want to go to your house?

4.No,I don't really like cartoons. I prefer movies.

=>Do you really like cartoon ?

5.She went to the doctor because she had a backache (Why)

=>Why did she go to the doctor ?

Chúc Bạn học tốt

Vì Ot là tia phân giác của AOB =>góc AOt =BOt=1/2.60=30 độ

OBz+OBy=180 độ (2 góc kề bù)

=>OBz =180-150=30 độ

=>By song song với Ot (vì OBz=BOt 2 góc so le trong )