35. Why don't we plant some trees around the schoolyard to get more fresh air?

36. I will telephone the station to make sure of the time of the train to Sa Pa.

37. What is his date of birth?

38. What is Miss Nga's address?

39. What about your home address?

40. Mr Tan is not as young as Miss Lien

B

D

C

A

gọi d=ƯCLN(5n+3;3n+2)

=> (5n + 3) chia hết cho d

=> 1 chia hết cho d

=> d = 1 (vì d thuộc N)

=> ƯCLN(5n + 3 ; 3n + 2) = 1

=> Phân số \(\frac{5n+3}{3n+2}\) tối giản với mọi n thuộc N.

duyệt trước rồi nộp bài nhé

23 T

24 F

25 F

26 F

27 T

28 caught

29 off

30 distance

31 speed

32 two

33 The bookshelves isn't low enough for me to reach

34 The children enjoyed walking in the rain

35 People used to travel to other countries on steamships

36 Mary drives at the same speed as Peter

        A =          \(\dfrac{1}{4^2}\) + \(\dfrac{1}{4^3}\) + ...........+ \(\dfrac{1}{4^{100}}\)

       A =          \(\dfrac{1}{4^2}\) +  \(\dfrac{1}{4^3}\)+...+ \(\dfrac{1}{4^{99}}\)+  \(\dfrac{1}{4^{100}}\)

4 \(\times\) A =   \(\dfrac{1}{4}\) + \(\dfrac{1}{4^2}\) + \(\dfrac{1}{4^3}\) +...+ \(\dfrac{1}{4^{99}}\)

4A - A =   \(\dfrac{1}{4}\) - \(\dfrac{1}{4^{100}}\)

      3A =  \(\dfrac{1}{4}\) - \(\dfrac{1}{4^{100}}\)

        A = ( \(\dfrac{1}{4}\) - \(\dfrac{1}{4^{100}}\)): 3

        A =   \(\dfrac{1}{12}\) - \(\dfrac{1}{3\times4^{100}}\)

Đặt A=1/4^2 +...+1/4^100

       4A=1/4+...+1/4^99

      4A-A=(1/4+...+1/4^99)-(1/4^2+...+1/4^100)

     3A=1/4-1/4^100

      A=(1/4-1/4^100)/3

Vậy...

Bài 2: 

Áp dụng tính chất của dãy tỉ số bằng nhau,ta được

\(\dfrac{a}{2}=\dfrac{b}{3}=\dfrac{c}{4}=\dfrac{a+b+c}{2+3+4}=\dfrac{45}{9}=5\)

Do đó: a=10; b=15;c=20

Câu nào bạn ơi