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NL
cho e hỏi bai này vs ạ mong mn lm giúp e e đang cần rất gấp
0
XT
0
MK
mn giúp e với á e đang cần gấp
2
13 tháng 4 2022
58.They have learned English since 2010.
59. It's time for you to go to school now.
60.She has bought that house since 5 years ago.
61.The car is too expensive for him to buy.
62. Who was this novel written by?
TH
13 tháng 4 2022
60&62 còn có thể có cách làm khác:
60.She has bought that house for 5 years.
62. Who was the author of this novel?
63. Lan is always forgetting her homework.
64. Tom is the worst Vietnamese speaker in his Vietnamese club.
65. Is the Temple of Literature surrounded by four busy streets?
66. Despite the rough sea, they still went to the island.
67. How far is it from your house to your school?
68, My brother used to go to school late when he was small.
69. Although it rained heavily, they still went out.
70. Some trees have been planted along the roads to the school by the children.
BB
1
30 tháng 9 2021
1) \(x^3+y^3+z^3-3xyz=\left(x^3+3x^2y+3xy^2+y^3\right)+z^3-3xyz-3x^2y-3xy^2=\left(x+y\right)^3+z^3-3xy\left(x+y+z\right)=\left(x+y+z\right)\left[\left(x+y\right)^2-\left(x+y\right)z+z^2\right]-3xy\left(x+y+z\right)=\left(x+y+z\right)\left(x^2+2xy+y^2-xz-yz+z^2\right)-3xy\left(x+y+z\right)=\left(x+y+z\right)\left(x^2+2xy+y^2-xz-yz+z^2-3xy\right)=\left(x+y+z\right)\left(x^2+y^2+z^2-xy-xz-yz\right)\)
2) Ta có: \(\left(a+b+c\right)^2=a^2+b^2+c^2\)
\(\Leftrightarrow a^2+b^2+c^2+2\left(ab+bc+ac\right)=a^2+b^2+c^2\)
\(\Leftrightarrow ab+bc+ac=0\)
\(\dfrac{1}{a^3}+\dfrac{1}{b^3}+\dfrac{1}{c^3}=\dfrac{3}{abc}\)
\(\Leftrightarrow\dfrac{a^3b^3+b^3c^3+a^3c^3}{a^3b^3c^3}=\dfrac{3}{abc}\)
\(\Leftrightarrow\dfrac{a^3b^3+b^3c^3+a^3c^3}{a^2b^2c^2}=3\)
\(\Leftrightarrow a^3b^3+b^3c^3+a^3c^3=3a^2b^3c^2\)
\(\Leftrightarrow\left(ab+bc\right)^3-3ab^2c\left(ab+bc\right)+a^3b^3-3a^2b^2c^2=0\)
\(\Leftrightarrow\left(ab+bc+ac\right)\left[\left(ab+bc\right)^2-\left(ab+bc\right)ac+a^2c^2\right]-3ab^2c\left(ab+bc+ac\right)=0\)
\(\Leftrightarrow0+0=0\left(đúng\right)\)
7 tháng 2 2022
\(1,7x-8=4x+7\)
\(\Leftrightarrow7x-8-4x=7\)
\(\Leftrightarrow7x-4x=7+8\)
\(\Leftrightarrow3x=15\)
\(\Rightarrow x=5\)
\(2,3-2x=3\left(x+1\right)-x-2\)
\(\Leftrightarrow3-2x=2x+1\)
\(\Leftrightarrow-2x+3=2x+1\)
\(\Leftrightarrow-2x-2x=1-3\)
\(\Leftrightarrow-4x=-2\)
\(\Rightarrow x=\dfrac{1}{2}\)
\(3,5\left(3x+2\right)=4x+1\)
\(\Leftrightarrow5.3x+5.2=4x+1\)
\(\Leftrightarrow15x+10=4x+1\)
\(\Leftrightarrow15x-4x=1-10\)
\(\Leftrightarrow11x=-9\)
\(\Rightarrow x=\dfrac{-9}{11}\)
cob = 140 ( hai góc đối đỉnh)
vì bod và doa lag hai góc kề bù
suy ra 180 - cob = 180- 140 = 40 độ
doa = aoc = 140 đọ hai góc đối đỉnh
LÝ THUYẾT:2 GÓC ĐỐI ĐỈNH(2 góc đối đỉnh thì bằng nhau)
2 GÓC KỀ BÙ:tổng 2 góc kề bù bằng 180 độ
Ta có 2 góc AOC bằng góc BOD mà tổng 2 góc bằng 140 độ nên COD=BOD=140/2=70 độ
Ta suy ra BOC=180-70=110 độ=>góc DOA=BOC=110 độ(2 góc đối đỉnh)