Giúp tui:
Cho A=131+132+133+...+159+160𝐴=131+132+133+...+159+160. Chứng...
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CM
14 tháng 4 2019
a ) 1 101 + 1 102 + 1 103 + ... + 1 149 + 1 150 > 1 150 + 1 150 + ... + 1 150 ⏟ 50 s o = 1 3
b ) 1 201 + 1 202 + ... + 1 400 < 1 200 + 1 200 + ... + 1 200 ⏟ 200 s o = 1
c) đặt S= 1 31 + ... + 1 40 + 1 41 + ... + 1 50 + 1 51 + ... + 1 60
S > 1 40 + .. + 1 40 ⏟ 10 s o + 1 50 + ... + 1 50 ⏟ 10 s o + 1 60 + ... + 1 60 ⏟ 10 s o = 1 40 + 1 50 + 1 60 = 37 60
M à 37 60 > 36 60 = 3 5 = > S > 3 5
S < 1 30 + .. + 1 30 ⏟ 10 s o + 1 40 + ... + 1 40 ⏟ 10 s o + 1 50 + ... + 1 50 ⏟ 10 s o = 10 30 + 10 40 + 10 50 = 47 60
M à 47 60 < 48 60 = 4 5 = > S < 4 5
PH
0
TN
5
6 tháng 1 2022
131.__The______TV is the most popular form of home entertainment.
132. ____Where____ will your future house be? I’m not sure . I may be in the mountains.
133.is/her mother/ going to buy/ a new house/ next month?
Is her mother going to buy a new house next month?
134. The simalar of “ start “ is “___ begin____”
135. He can’t ___get ____up early because he_stay___ up late yesterday.
136.grasshopper_______ ( hinh con châu chấu)
137.or you may / at TV/ Lower/ have an earache./ the volume
Lower the volume at TV or you may have an earache.
138.Odd one out:
A. Hide- and-seek B.blind man’s bluff C. festival D. skipping
139.vacation/ Linh/ spent/ her summer/ in Da Nang.
Linh spent her summer vacation in Da Nang.
140.I don’t /my cat./ Do/ you know/ where it is?/ find
I don't find my cat. Do you know where it is?
141.to keep him warm/ and wrap him/in a blanket./ a hot drink/ Make him
Make him a hot drink to keep him warm and wrap him in a blacket.
142.___the end, they got married and lived happily ever after.
A. at B.On C. In D. During
143.Your room is in a mess. Let’s ____________.
A. clean up B. Come here C. count the sheep D. make a circle
144.when/ rains./ Bring /it/ our umbrella
Bring our umbrella when it rains.
145.with her family./ last weekend she/ went on a picnic/ Linda wasn’t/ at the party
Linda wasn't at the party last weekend. She went on a picnic with her family.
146.The kife is very sharp___ and you can hurt yourself.
147.The mother/ the clothes/garering/ together/ is …
The mother is garthering the clothes together.
DT
6 tháng 1 2022
131. watching
132. where
133. Is her mother going to buy a new house next month?
134. begin
135. get/ stayed
136. grasshopper
137. Lower the volume at TV or you may have an earache.
138. C
139. Linh spent her summer vacation in Da Nang.
140. I don’t find my cat. Do you know where it is?
141. Make him a hot drink and wrap him in a blanket to keep him warm.
142. C
143. A
144. Bring our umbrella when it rains.
145. Linda wasn’t at the party last weekend she went on a picnic with her family.
NT
Nguyễn Thị Thương Hoài
Giáo viên
VIP
7 tháng 4 2023
A = 13 + 132 + 133 + 134 + 135 + 136
A = (13 + 132) + ( 133 + 134) + (135 + 136)
A = 13 \(\times\) ( 1 + 13) + 133 \(\times\) ( 1 + 13) + 135 \(\times\) ( 1 + 13)
A = 13 \(\times\) 14 + 133 \(\times\) 14 + 135 \(\times\) 14
A = 14 \(\times\) ( 13 + 133 + 135) vì 14 ⋮ 2
⇒ A ⋮ 2 ( đpcm)
Lời giải:
$A=(\frac{1}{31}+\frac{1}{32}+...+\frac{1}{39})+(\frac{1}{40}+\frac{1}{41}+....+\frac{1}{49})+(\frac{1}{50}+....+\frac{1}{59})+\frac{1}{60}$
$< \frac{9}{30}+\frac{10}{40}+\frac{10}{50}+\frac{1}{60}=\frac{23}{30}< \frac{4}{5}$