a)S=1+5+52+53+54+55+56+57+58
S=1-5+52-53+54-55+56-57+58
(làm nhanh giùm mình mình like cho)
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50) \(\sqrt{98-16\sqrt{3}}=4\sqrt{6}-\sqrt{2}\)
51) \(\sqrt{2-\sqrt{3}}=\dfrac{\sqrt{4-2\sqrt{3}}}{\sqrt{2}}=\dfrac{\sqrt{3}-1}{\sqrt{2}}=\dfrac{\sqrt{6}-\sqrt{2}}{2}\)
52) \(\sqrt{4+\sqrt{15}}=\dfrac{\sqrt{8+2\sqrt{15}}}{\sqrt{2}}=\dfrac{\sqrt{5}+\sqrt{3}}{\sqrt{2}}=\dfrac{\sqrt{10}+\sqrt{6}}{2}\)
53) \(\sqrt{5-\sqrt{21}}=\dfrac{\sqrt{10-2\sqrt{21}}}{\sqrt{2}}=\dfrac{\sqrt{14}-\sqrt{6}}{2}\)
54) \(\sqrt{6-\sqrt{35}}=\dfrac{\sqrt{12-2\sqrt{35}}}{\sqrt{2}}=\dfrac{\sqrt{14}-\sqrt{10}}{2}\)
55) \(\sqrt{2+\sqrt{3}}=\dfrac{\sqrt{4+2\sqrt{3}}}{\sqrt{2}}=\dfrac{\sqrt{6}+\sqrt{2}}{2}\)
56) \(\sqrt{4-\sqrt{15}}=\dfrac{\sqrt{8-2\sqrt{15}}}{\sqrt{2}}=\dfrac{\sqrt{10}-\sqrt{6}}{2}\)
số số hạng có trong biểu thức trên là:
(58 - 40 ) : 1 + 1 = 19
=>( 40 - 41 ) + ( 42 - 43 ) + ... + ( 56 - 57 ) + 58
=> (-1) x [( 19 - 1 ) : 2 ] + 58
=> (-1) x 9 + 58
=> (-9) + 58
=> 49
HT~~~
Đú đởn ăn chơi học hành sa sút đến nỗi có bài toán đơn giản như zậy mà cũng phải hỏi !
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
ta có: 2005 + 53-54-55+56-57-58-59+60+61-62-63+64+65-66-67+68+69
= 2005+(53-54-55+56)+(57-58-59+60)+(61-62-63+64)+(65-66-67+68)+69
= 2005+0+0+0+0+69
= 2005+69
= 2074
52. They told me a lie, ___didn't they____?
53. It cant be so bad, __can it____?
54. They had to arrive on time, ___didn't they_____?
55. Shed better go to sleep early, ____hadn't she______?
56. It was a pity, ___wasn't it____?
57. You mustn't do that again, ____must you_____?
58. He must be your good friend, ___mustn't he______?
59 The woman seldom writes poems and stories, ________does she___?
52.didn't they
53.can it
54.didn't they
55.hadn't she
56.wasn't it
57.must you
58.mustn't he