Câu 87:
Don't ____late.
Ai làm được bài này ko
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NV
Nguyễn Việt Lâm
Giáo viên
22 tháng 6 2021
84.
Ta có: \(\left\{{}\begin{matrix}SA\perp\left(ABC\right)\Rightarrow SA\perp BC\\BC\perp AB\left(gt\right)\end{matrix}\right.\) \(\Rightarrow BC\perp\left(SAB\right)\Rightarrow BC\perp SB\) đồng thời SB là hình chiếu vuông góc của SC lên (SAB)
\(\Rightarrow\widehat{BSC}\) là góc giữa SC và (SAB)
\(\Rightarrow\widehat{BSC}=30^0\)
\(\Rightarrow SB=\dfrac{BC}{tan30^0}=a\sqrt{3}\)
\(\Rightarrow SA=\sqrt{SB^2-AB^2}=a\sqrt{2}\)
\(V=\dfrac{1}{3}SA.BC^2=\dfrac{a^3\sqrt{2}}{3}\)
NV
Nguyễn Việt Lâm
Giáo viên
22 tháng 6 2021
87.
Gọi M là trung điểm BC \(\Rightarrow AM\perp BC\) (trung tuyến đồng thời là đường cao trong tam giác cân)
Mà \(SA\perp\left(ABC\right)\Rightarrow SA\perp BC\)
\(\Rightarrow BC\perp\left(SAM\right)\)
Lại có BC là giao tuyến (SBC) và (ABC)
\(\Rightarrow\widehat{SMA}\) là góc giữa (SBC) và (ABC)
\(\Rightarrow\widehat{SMA}=60^0\)
\(AM=\sqrt{AB^2-BM^2}=\sqrt{4a^2-\left(\dfrac{3a}{2}\right)^2}=\dfrac{a\sqrt{7}}{2}\)
\(SA=AM.tan60^0=\dfrac{a\sqrt{21}}{2}\)
\(V=\dfrac{1}{3}SA.\dfrac{1}{2}.AM.BC=\dfrac{7a^3\sqrt{3}}{8}\)
23 tháng 1 2017
43.(87-26)-87.(26-43)
=43.87-43.26-87.26+87.43
=43.87-87.43+43.26-87.26
=0+26.(43-26)
=26.17
=442
CM
18 tháng 3 2018
Đáp án cần chọn là: C
Trong phép trừ 231−87thì 231 là số bị trừ và 87 là số trừ nên C đúng.
HV
8 tháng 12 2021
83. She is too old to have any more children. (wish)
She wishes she weren't old and could have some more children
84. I don't smoke any longer. (used to)
I used to smoke
85. Although she was not beautiful, she took part in a beauty contest. (but)
She was not beautiful, but she took part in a beauty contest.
86. "I take you to town," Ann said to John. (offer)
Ann offered to take John to town
87. He got rid of drinking two years ago. (give up)
He gave up drinking two years ago
88. We can't go out because of the heavy rain. (because)
We can't go out because it rains heavily
89. This flat is too small for three people. (enough)
This flat is not large enough for three people
90. " You mustn't leave the door unlocked," Mr. Atkins said to Mark. (told)
Mr Atkins told Mark not to leave the door unlocked
91. D espite knowing this place very well, I got lost. (though)
I__got lost although I knew this place very well
92. " I'll finish it by the end of this week," he said. (promise)
He promised to finish it by the end of that week
93. " Would you like to come on a picnic with us?" Mike said to me. (invite)
Mike invited me to come on a picnic with them
94. " Don't wear those boots in the house," she said to her child. (ask)
She asked her child not to wear these boots in the house
MH
10 tháng 10 2014
câu 1 86-x=33
x=86-33
x=53
vậy x=53
câu 2 53+(124-x)=87
53+124-x=87
x=53+124-87
x=90
vậy x=90
27 tháng 10 2016
nhan xet ho to dung chua nha
53+(124-x)=87
(124-x)=87-53
x=124-34
=90
TT
2 tháng 9 2020
Ta có :
\(\frac{x-3}{97}+\frac{x-27}{73}+\frac{x-67}{33}+\frac{x-73}{27}=4\)
\(\Leftrightarrow\left(\frac{x-3}{97}-1\right)+\left(\frac{x-27}{73}-1\right)+\left(\frac{x-67}{33}-1\right)+\left(\frac{x-73}{27}-1\right)=0\)
\(\Leftrightarrow\frac{x-100}{97}+\frac{x-100}{73}+\frac{x-100}{33}+\frac{x-100}{27}=0\)
\(\Leftrightarrow\left(x-100\right)\left(\frac{1}{97}+\frac{1}{73}+\frac{1}{33}+\frac{1}{27}\right)=0\)
Vì \(\frac{1}{97}+\frac{1}{73}+\frac{1}{33}+\frac{1}{27}>0\) Nên \(x-100=0\)
\(\Leftrightarrow x=100\)
Vậy \(x=100\)
2 tháng 9 2020
\(\Leftrightarrow\frac{x-3}{87}+\frac{x-27}{79}+\frac{x-67}{33}+\frac{x-73}{27}-4=0\)
\(\Leftrightarrow\left(\frac{x-3}{97}-1\right)+\left(\frac{x-27}{73}-1\right)+\left(\frac{x-67}{33}-1\right)+\left(\frac{x-73}{27}-1\right)=0\)
\(\Leftrightarrow\left(\frac{x-3-97}{97}\right)+\left(\frac{x-27-73}{73}\right)+\left(\frac{x-67-33}{33}\right)+\left(\frac{x-73-27}{27}\right)=0\)
\(\Leftrightarrow\frac{x-100}{97}+\frac{x-100}{73}+\frac{x-100}{33}+\frac{x-100}{27}=0\)
\(\Leftrightarrow\left(x-100\right)\left(\frac{1}{97}+\frac{1}{73}+\frac{1}{33}+\frac{1}{27}\right)=0\)
Vì \(\frac{1}{97}+\frac{1}{73}+\frac{1}{33}+\frac{1}{27}\ne0\)
\(\Rightarrow x-100=0\Leftrightarrow x=100\)
be
Don't __be__late