14 B

15 B

16 D

17 A

18 A

19 A

20 A

14.A

15.B

16.D

17.A

18.A

19.A

20.A

Chọn C

Thi đúng hong bạn:D

C

11. Can't you ?

12. Did we ?

13. Didn't they ?

14. Doesn't she ?

15. Have you ?

16. Will she ?

17. Is it ?

18. Shall we ?

19. Shall we ?

20. Do you ? 

Câu 20:

\(S=\frac{2}{1.4.7}+\frac{2}{4.7.10}+...+\frac{2}{34.37.40}\)

\(3S=\frac{6}{1.4.7}+\frac{6}{4.7.10}+....+\frac{6}{34.37.40}=\frac{7-1}{1.4.7}+\frac{10-4}{4.7.10}+...+\frac{40-34}{34.37.40}\)

\(=\frac{1}{1.4}-\frac{1}{4.7}+\frac{1}{4.7}-\frac{1}{7.10}+...+\frac{1}{34.37}-\frac{1}{37.40}\)

\(=\frac{1}{1.4}-\frac{1}{37.40}=\frac{369}{1480}\)

$S=\frac{123}{1480}$

\(A=\left(\dfrac{\sqrt{a}+1}{\sqrt{a}-1}-\dfrac{\sqrt{a}-1}{\sqrt{a}+1}+4\sqrt{a}\right)\left(\sqrt{a}+\dfrac{1}{\sqrt{a}}\right)\left(a>0,a\ne1\right)\)

\(A=\left[\dfrac{\left(\sqrt{a}+1\right)^2}{a-1}-\dfrac{\left(\sqrt{a}-1\right)^2}{a-1}+4\sqrt{a}\right].\left(\dfrac{a+1}{\sqrt{a}}\right)\)

\(A=\left[\dfrac{\left(\sqrt{a}+1+\sqrt{a}-1\right)\left(\sqrt{a}+1-\sqrt{a}+1\right)}{a-1}+\dfrac{4\sqrt{a}\left(a-1\right)}{a-1}\right].\dfrac{a+1}{\sqrt{a}}\)

\(A=\left[\dfrac{4\sqrt{a}+4\sqrt{a}\left(a-1\right)}{a-1}\right].\dfrac{a+1}{\sqrt{a}}\)

\(A=\left[\dfrac{4\sqrt{a}\left(1+a-1\right)}{a-1}\right].\dfrac{a+1}{\sqrt{a}}\)

\(A=\dfrac{\left(4a\sqrt{a}\right)\left(a+1\right)}{\left(a-1\right)\sqrt{a}}=\dfrac{4a\left(a+1\right)}{a-1}=\dfrac{4a^2+4a}{a-1}\)

bằng 1220 nha

=1220 nha nhớ cho milk 1 k nhé

=1200 , k nha ko đc quênnnnn

60% mình tk rồi đó

60% tk mình nha

60%

k nhé

Mắc gì phải viết(chắc bạn giỏi mà bảo người khác ko giỏi)

Ha Quynh Nhu noi dung

:)