Giải thích tại sao những người bị thiếu máu lên não thường bị chóng mặt?

Tại sao cây hoa tinh nữ có thể úp lá lại khi có một tác động từ bên ngoài ?

Chọn B

a) Xét △ABC và △HBA có:

góc BAC = góc BHA = 90 độ

góc B chung

⇔ △ABC ∼ △HBA (g.g) (1)

⇔ AB/BC = HB/AB

⇒ AB² = BC . BH (đpcm)

Xét △ABC và △HAC có:

góc BAC = góc AHC = 90 độ

góc C chung

⇔ △ABC ∼ △HAC (g.g) (2)

⇔ AB/BC = HA/AC

⇒ AB.AC=BC.AH (đpcm)

Từ (1),(2) ⇒ △ABH ∼ △CAH

⇒AH/BH=HC/AH

⇒ AH²= BH. HC (đpcm)

Cho △ABC vuông ở A, vẽ AH ⊥ BC, AD là phân giác góc A. C/m:

a) AH² = BH . CH AB . AC = BC . AH

AB² = BH . BC

b) Cho AB = 5 cm, AC = 12 cm. Tính BD, DC, AH, BH.

c) Tính tỉ số diện tích △AHB và △ABC

Viết lại câu:

1. Lan doesn't cook well and Mai doesn't, either.

⇒ Neither...............................................................

2. The garage is going to repair the car for us next week.

⇒ We are going ...................................................

3. She didn't say a word as she left the room.

⇒ She left the room ............................................

4. The storm blew a lot of trees down last night.

⇒ A lot ..................................................................

5. She is proud of her son's contribution to the play.

⇒ She is proud of what ................................................

6. I could realize how important the family is only after I left home.

⇒ Not until ..................................................................

7. It was wrong of you to allow your child to walk home alone.

⇒ You should ...............................................................

Dùng từ gợi ý viết câu:

1. Who broke the window ? (By)

2. When the Prime Minister was asked about the strike, he declined to comment. (On)

3. She wore dark glasses so that noone could recognize her. (avoided)

4. There were lots of people in the hall. (was)

5. I've never met such a nice girl than Loan. (the)

6. The tea was so hot that couldn't drink it. (such)

7. I haven't seen you for 2 years. (It)

8. "You were cheating" said Carol to June. (accused)

9. You don't need to do it. (isnot)

10. I'm not used to getting up early. (habit)

PTHH: CuO + H₂ → Cu + H₂O (thêm nhiệt độ)

Theo bài ra, ta có:

n_CuO = m/M = 8 / 80 = 0,1 (mol)

Theo PTHH, ta có:

n_Cu = n_CuO = 0,1 (mol)

⇔ m_Cu = n . M = 0,1 . 65 = 6,5 (g)