Câu 5:
2/a 
Ta có: \(\widehat{aBC}=\widehat{BCb'}(=72^o)\)
Mà \(\widehat{aBC} \) và \(\widehat{BCb'}\) ở vị trí so le trong 
\(\Rightarrow aa'//bb'\)

Câu 6:
a) Ta có: \(a\perp c\)
               \(b\perp c\)
\(\rightarrow a//b \) hay \(AB//CD \) (1)
b) Từ (1) \(\rightarrow \widehat{ABC}+\widehat{BCD}=180^o\) (2 góc trong cùng phía)
              \(\rightarrow \widehat{ABC}+72^o=180^o\)
              \(\rightarrow \widehat{ABC}=180^o -72^o =108^o\)
c) Vì BE là tia phân giác của \(\widehat{ABC}\)
\(\rightarrow \widehat{ABE}=\widehat{EBC}\)
\(\rightarrow \widehat{ABE}=\dfrac{1}{2}\widehat{ABC}=\dfrac{1}{2}108^o=54^o\)

Ta có: \(\widehat{AOB}=\dfrac{1}{5}\widehat{AOC}\)

Mà \(\widehat{AOC}=80^o(GT)\)
\(\Rightarrow \widehat{AOB}=80^o.\dfrac{1}{5}=16^o\)

Lại có: \(\widehat{BOC}=\widehat{AOC}+\widehat{AOB}\) 
                 \(\rightarrow\widehat{BOC}=80^o+16^o\)
                 \(\rightarrow\widehat{BOC}=96^o\)

Cái trên chỉ áp dụng với phép nhân nên cách làm của bạn sai rồi.

33. Nam likes playing computer games.
34. My sister and I love outdoor activities.
35. I spent three hours making this pottery.
36. My house on the street is the oldest house.

1. We joined many community activities to help needy people last summer.
2. Joy makes you strong and reduces stress.
3. Air pollution is really harmful to our health.
4. Going to bed and getting up early is good for your health.

/ʃ/: share, action, national, wish, competition
/ʒ/: usual, leisure, vision, Asia, musican, measure, television

6,52

How - dentist - destroy - brush - before - for - and - such - because 

B