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Câu 9: Tính bằng cách thuận tiện nhất
102 + 7 +243 + 98
= (102 + 98) + (7 + 243)
= 200 + 250
= 450
Bài 1
5kg 35g = 5035kg
1 tạ 50kg < 150 yến
9600 giây = 200 phút
10 thế kỷ = 10000 năm
Bài 2
102 + 7 + 243 + 98
= (102+98)+(243+7)
= 200 + 250
= 450
pạn nào giải giúp mình bài này trước 16h đc ko ( mình năn nỉ đó )
\(\left\{{}\begin{matrix}SA\perp\left(ABC\right)\Rightarrow SA\perp BC\\AB\perp BC\left(gt\right)\end{matrix}\right.\) \(\Rightarrow BC\perp\left(SAB\right)\)
Lại có \(BC\in\left(SBC\right)\Rightarrow\left(SBC\right)\perp\left(SAB\right)\)
3 C
4 B
5 A
6 B
7 A
8 A
9 C
10 D
11 B
12 B
13 A
14 C
15 B
16 A
17 D
18 D
19 C
20 A
21 B
22 B
23 C
24 D
25 B
26 D
27 A
28 D
29 C
30 B
31 C
32 A
33 A
Viết lại câu
12
Authorities in Ho Chi Minh City suggested that current school break schould be extended by us until the end of March to control the epidemic caused by Covid-19
15 The plumber who has just been had check the pipes in my house is very skillful
16 In spite of the fact that we had invited her to the party, she didn't come
17 Since they didn't have a map, they lost their way
18 I suggest that energy-saving bulbs should be used to reduce the electricity bill
19 We are looking forward to seeing your gook action from your company
20 Linda congratulated Owen on scoring a wonderful goal
21 She had all the water pipes in her house checked by the plumber yesterday
22 If you go on smoking, you will be seriously sick
23 I suggested all the bag should be collected and taken to the garbage dump
24 If you aren't carefull, you will fall over the rocks
25 If you work too much, you will feel tired
26 If you are careless, you'll break the vase
\(A=\left(\frac{x}{x+2}+\frac{x^3}{\left(x+2\right)\left(x^2-2x+4\right)}.\frac{x^2-2x+4}{4-x^2}\right):\frac{4}{x+2}\)
\(A=\left(\frac{x}{x+2}+\frac{x^3}{x+2\left(4-x^2\right)}\right):\frac{4}{x+2}\)
\(A=\left(\frac{4x-x^3+x^3}{x+2\left(4-x\right)}\right):\frac{4}{x+2}\)
\(A=\frac{4x}{x+2\left(4-x\right)}.\frac{x+2}{4}\)
\(A=\frac{x}{4-x}\)
\(b,\frac{x}{4-x}>0\)
xét 2 trường hợp x>0 đồng thời 4-x>0 (điều kiện x\(\ne\)4) và x<0 ,4-x<0
\(TH1:0< x< \text{4}\)
\(TH2:\)ko có giá trị x
\(c,Ax=\frac{x}{4-x}x\)=\(\frac{x^2}{4-x}\)
\(\frac{x^2-16+16}{4-x}\)
\(\frac{\left(x-4\right)\left(x+4\right)+16}{4-x}\)
\(-\left(x+4\right)+\frac{16}{4-x}\)
để AX nguyên thì \(16⋮4-x\)
lập bảng ra tìm đc x = 0,2,-4,-12,5,6,8,12,20
A=\(\frac{1}{20}+\frac{1}{30}+\frac{1}{42}+\frac{1}{56}+\frac{1}{72}+\frac{1}{90}\)
A= \(\frac{1}{4\times5}+\frac{1}{5\times6}+\frac{1}{6\times7}+\frac{1}{7\times8}+\frac{1}{8\times9}+\frac{1}{9\times10}\)
A=\(\frac{1}{4}-\frac{1}{5}+\frac{1}{5}-\frac{1}{6}+\frac{1}{6}-\frac{1}{7}+\frac{1}{7}-\frac{1}{8}+\frac{1}{8}-\frac{1}{9}+\frac{1}{9}-\frac{1}{10}\)
\(\Rightarrow A=\frac{1}{4}-\frac{1}{10}\)
\(A=\frac{3}{20}\)
\(A=\frac{1}{20}+\frac{1}{30}+\frac{1}{42}+\frac{1}{56}+\frac{1}{72}+\frac{1}{90}\)
\(A=\frac{1}{4.5}+\frac{1}{5.6}+\frac{1}{6.7}+\frac{1}{7.8}+\frac{1}{8.9}+\frac{1}{9.10}\)
\(A=\frac{5-4}{4.5}+\frac{6-5}{5.6}+\frac{7-6}{6.7}+\frac{8-7}{7.8}+\frac{9-8}{8.9}+\frac{10-9}{9.10}\)
\(A=\frac{1}{4}-\frac{1}{5}+\frac{1}{5}-\frac{1}{6}+\frac{1}{6}-\frac{1}{7}+\frac{1}{7}-\frac{1}{8}+\frac{1}{8}-\frac{1}{9}+\frac{1}{9}-\frac{1}{10}\)
\(A=\frac{1}{4}-\frac{1}{10}=\frac{3}{20}\)