KHO THE

\(A=\frac{\left[\left(25-1\right):1+1\right]\left(25+1\right)}{2}=325.\)

\(B=\frac{\left[\left(51-3\right):2+1\right]\left(51+3\right)}{2}=675\)

\(C=\frac{\left[\left(81-1\right):4+1\right]\left(81+1\right)}{2}=861\)

1, The homework is too difficult for him to do

2, The homework isn't easy enough for him to do

3, The homework is so difficult that he can't do it

4, It is such difficult homework that he can't do it

1. My sister says she went to school by bus this morning.

    My sister said she had gone to school by bus that morning.

2. Nga says she have done her homework.

    Nga said she had done her homework.

1, My sister says that she goes to school by bus this morning

My sister said that she had gone to school by bus this morning

2, Nga says that she have done her homework

Nga said that she had done her homework

1A

2C

3B

4B

5D

6A

7B

8A

9B

10B

is a big supermarket next to our school

not met him for 3 months

10-day Tet holiday

d: \(\Leftrightarrow x+5=5\)

hay x=0