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5 tháng 2 2020

CÂU NÀY BÀI MẤY SÁCH LỚP 12 VẬY BẠN

5 tháng 2 2020

Câu này ko có trong sách lớp 12 đâu vì cô mk giao mà....

4 tháng 2 2020

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4 tháng 2 2020

Thui khỏi bt lm òi * nhắn lun ko bt cho nhanh lại cn lm màu *

21 tháng 8 2019

Khối đa diện đều loại  5 ; 3 là khối mười hai mặt đều

gồm 12 mặt là các ngũ giác đều nên tổng các góc bằng 12 . 3 π = 36 π (mỗi mặt chia thành 5 tam giác để tổng góc)

Chọn đáp án B

10 tháng 12 2019

* Gọi a là số cạnh, b là số mặt của khối đa diện.

Nếu khối đa diện có các mặt là tam giác thì mỗi mặt có ba cạnh. Trong ba cạnh đó mỗi cạnh lần lượt là cạnh chung của hai mặt.

Ta có 3b = 2a. Nghĩa là b chẵn.

Mà 2a chia hết cho 2 nên 3b cũng chia hết cho 2

⇒ b chia hết cho 2 hay b là số chẵn.

* Ví dụ: hình tứ diện đều có 4 mặt

Giải bài 1 trang 12 sgk Hình học 12 | Để học tốt Toán 12

 

1 tháng 4 2017

Giả sử đa diện (H) có m mặt. Vì mỗi mặt của (H) có 3 cạnh, nên m mặt có 3m cạnh. Nhưng mỗi cạnh của (H) là cạnh chung của đúng hai mặt nên số cạnh của (H) bằng c = \(\dfrac{3m}{2}\). Do c là số nguyên dương nên m phải là số chẵn. Ví dụ : Số cạnh của tứ diện bằng sáu.

T
Tester
CTVVIP
5 tháng 7

Xuất sắc

11 tháng 4 2017

Giải sách bài tập Toán 12 | Giải sbt Toán 12

Xét hai đường sinh SA , SB tùy ý của hình nón. Vẽ đường kính AC của đường tròn đáy. Ta có góc ASC là góc ở đỉnh của hình nón. Hai tam giác ASC và ASB có hai cặp cạnh bằng nhau vì chúng cùng là đường sinh của hình nón.

Ta có cạnh AC ≥ AB nên  ∠ ASC  ≥   ∠ ASB. Đó là điều cần chứng minh.

22 tháng 5 2017

Mặt cầu, mặt nón tròn xoay và mặt trụ tròn xoay