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27 tháng 12 2017
Đú đởn ăn chơi học hành sa sút đến nỗi có bài toán đơn giản như zậy mà cũng phải hỏi !
27 tháng 12 2017
40-41+42-43+44-45+46-47+48-49+50-51+52-53+54-55+56-57+58=
=40+(42-41)+(44-43)+(46-45)+(48-47)+(50-49)+(52-51)+(54-53)+(56-55)+(58-57)=49
TT
2
HT
0
BD
4
KD
31 tháng 7 2016
55^(n+1) -55^n
= 55^n.55 -55^n
=55^n( 55 - 1)
=55^n.54 luôn luôn chia hết cho 54 ( do tích có 1 thừa số là 54)
S
6 tháng 7 2019
a, 1 + 2 + 3 + ... + 87
= (1 + 87).87 : 2
= 87.88 : 2
= 87.44
= 3828
b, 2 + 4 + 6 + ... + 54
= (2 + 54).27 : 2
= 27.56 : 2
= 27.28
= 756
c, 3 + 6 + 9 + ... + 99
= (99 + 3).49 : 2
= 49.102 : 2
= 49.51
= 2499
d, 45.25 + 45.75 + 55.25.25 + 55.75
= 45. (25 + 75) + 55(25.25 + 75)
= 45.100 + 55.700
= 4500 + 38500
= 43000
6 tháng 7 2019
\(d,45x25+45x75+55x25+55x75\)
\(=45x\left(25+75\right)+55x\left(25+75\right)\)
\(=45x100+55x100\)
\(=100x\left(45+55\right)\)
\(=100x100\)
\(=10000\)
DT
Đỗ Thanh Hải
CTVVIP
28 tháng 7 2021
VI. Cho dạng đúng của từ in hoa trong ngoặc.
53. This is one of the……worst…….films I’ve ever seen. ( BAD )
54. I’m Vietnamese. What’s your………nationality………. ( NATION )
55. Hung is a very safe………driver…… ( DRIVE )
59. Edison’s most famous ……invention…. was the electronic bulb. (INVENT)
60. You should do morning exercises to have a……healthy…....body.( HEALTH)
61. There are about 200 ……employees…….in this company. (EMPLOY)
62. Mai studies English very ……well……………. ( GOOD)
63. .Linda is the most........beautiful...... of the two girls. ( BEAUTY)
64. The most popular …actvity……….. at recess is talking . (ACT)
65. Hoa is having a............medical.......check-up. (MEDICINE)
VII. Viết lại các câu sau đây sao cho nghĩa không thay đổi.
66. Linh is eleven years old. Mai is twelve years old
àMai is……older than Linh…………………………………………………….............……….…….
67. Going to the cinema is better than reading books at home.
àI prefer……Going to the cinema to reading books at home………………………………………………………………………….
68. Hong Son is a very good soccer player.
àHong Son Plays……football well………………………………………………………………...
69. Who is the owner of this book ?
àWho does……this book belong to……………………………………………………………………….
70.Mount Everest is the hihgest mountain in the world.
àNo mountain…in the world is as high as Mount Everest ………………………………………………………………….….
71. February often has 28 days.
àThere ……are often 28 days in February……………………………………………………………………….….
72. What a luxurious car!
àHow……luxurious the car is……………………………………………………………………….….!
73. It takes me an hour to do my homework every evening.
àI spend ……an hour doing my homework every evening.………………………………………………………………….….…
74. What is the price of this cap ?
à How much........does this cap cost...............................................................…………………….…...?
75. Finding an apartment in a big city is not easy.
àIt is ……not easy to find an apartment in a big city ……………………………………………………….……………………
VIII. Hoàn thành các câu sau dùng từ cho sẵn:
76. Would/ like/ go/ movie theater/ me/ tonight ?
……………Would you like to go to the movie theater with me tonight…………………………………………………………………………..?
77. You / ought / not/ drink/ coffee /because/ it/ not/ good/ you.
…………You ought not to drink coffee because it is not good for you……………………………………………………………………………..
78. It/ take/ he/ 30 minutes/ go/ Ky Anh town/ motorbike.
…………It takes him 30 min to go to Ky Anh town by motorbike ………………………………………………………………………………..
79. My home land/ tobe/ different/ yours.
…………My homeland is different from yours……………………………………………………………………………..
80. Could/show/me / how/ to/ get/ post office/ , please ?
…………Could you show me how to get to the post office please……………………………………………………………………………..
81. Ba/ interested/ collect/ stamps.
………Ba is interested in collecting stamp………………………………………………………………………………..
82. Lastnight,/ Mr. Lam/ watch/ interesting/ film/ TV
…………Last night, Mr Lam watched an interesting film on TV……………………………………………………………………………..
83. They/ rehearse/ play/ the school anniversary/ celebration/ at present.
…………They are rehearsing play for the school annyversary velebration at present……………………………………………………………………………..
84. She/ usually/ go/ library/ her free time.
……………She usually goes to the library on the free time…………………………………………………………………………..
85. There/ tobe/ one/ table/ four chairs/ dining-room.
…………There is one table and 4 chairs in the dining room……………………………………………………………………………..
54:
Gọi O là giao của AC và BD
ABCD là hình thoi
=>AC vuông góc BD tại O và O là trung điểm chung của AC và BD
\(\widehat{BAD}=180^0-120^0=60^0\)
Xét ΔABD có AB=AD và góc BAD=60 độ
nên ΔABD đều
=>\(AO=AB\cdot\dfrac{\sqrt{3}}{2}\)
=>\(AG=\dfrac{2}{3}\cdot AO=\dfrac{\sqrt{3}}{3}\cdot a\)
\(AA'=\sqrt{a^2-\left(\dfrac{a\sqrt{3}}{3}\right)^2}=\dfrac{a\sqrt{6}}{3}\)
\(S_{ABCD}=2\cdot S_{ABD}=AB\cdot AD\cdot sinBAD=\dfrac{a^2\sqrt{3}}{2}\)
\(V=\dfrac{a\sqrt{6}}{3}\cdot\dfrac{a^2\sqrt{3}}{2}=\dfrac{a^3\sqrt{2}}{2}\)
=>Chọn C
55:
ΔABC vuông tại B
=>\(S_{ABC}=\dfrac{1}{2}\cdot a\sqrt{3}\cdot a=\dfrac{a^2\sqrt{3}}{2}\)
\(V_{S.AHK}=\dfrac{1}{4}\cdot V_{ABC}=\dfrac{1}{4}\cdot\dfrac{1}{3}\cdot a\cdot\dfrac{a^2\sqrt{3}}{2}=\dfrac{a^3\sqrt{3}}{30}\)
=>B