Bài 1:

\(1-4+7-10+...-100+103\)

\(=\left(1-4\right)+\left(7-10\right)+...+\left(97-100\right)+103\)

\(=\left(-3\right)+\left(-3\right)+...+\left(-3\right)+103\)

(17 số hạng -3)

\(=-3\cdot17+103\)

\(=52\)

didn't

1. They ( not have )don't have a board.

2. She ( wash )washes the dishs.

3. Does He ( stay )stay at home ?

4. What does he do( do ) ?

5. When do you ( have )have lunch ?

6. Who lives( live ) on DN street ?

7. Where do you ( live )live ?

8. Does Nam ( wash )wash his face ?

9. Mary ( have )has a brother.

Từ O kẻ OC // a

mà a // b (gt)

Do đó OC // a // b

=> A = AOC (2 góc so le trong)

và B = BOC (2 góc so le trong)

Do đó AOC = 30^o, BOC = 45^o

Ta có: OC nằm giữa OA, OB

=> AOC + BOC = AOB

=> 30^o + 45^o = AOB

=> AOB = 75^o

Bài 1:

a) Vì a // b mà a \(\perp\) b (gt)

=> c \(\perp\) b (quan hệ từ vuông góc đến song song)

b) Ta có: D1 + D2 = 180^o (2 góc kề bù)

=> D2 = 121^o

mà a // b (gt)

Do đó: D2 = C2 (2 góc so le trong)

=> C2 = 121^o

so cay hong xiem la :

             35 x 1/7= 5 cay 

so cay nhan va cay vai la :

            35-5= 30 cay 

vi so cay vai = so cay nhan nen so cay nhan la :

           30:2= 15 cay

                  D/S : 15 cay

Nhiều lắm

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