rút gọn biểu thức

a) A= \(2\sqrt{\frac{1}{2}}+\sqrt{18}\)

b) B= \(\frac{5+3\sqrt{5}}{\sqrt{5}}+\frac{3+\sqrt{3}}{\sqrt{3}+1}-\left(\sqrt{5+3}\right)\)

c) C= \(\frac{1}{x+\sqrt{x}}+\frac{2\sqrt{x}}{x-1}-\frac{1}{x-\sqrt{x}}\left(x>0,x\ne1\right)\)

d) D = \(\left(\frac{\sqrt{x}+2}{x+2\sqrt{x}+1}-\frac{\sqrt{x-2}}{x-1}\right)\left(x+\sqrt{x}\right)\left(x>0,x\ne1\right)\)

e) E = \(\frac{2+\sqrt{3}}{\sqrt{2}+\sqrt{2+\sqrt{3}}}+\frac{2-\sqrt{3}}{\sqrt{2}-\sqrt{2-\sqrt{3}}}\)

Tìm điều kiện xác định của những biểu thức sau :

a) \(\sqrt{\frac{3}{\left(x+1\right)^2}}\)

b) \(\sqrt{\frac{-1}{x^2+2}}\)

c) \(\sqrt{x^2+4x+5}\)

d) \(\sqrt{\frac{x-3}{x+4}}\)

1. They (be) ............ my best friends for ten years.

2. Why he (go) ............ to school late this morning ?

- Because he (stay) ............. up late last night

3. That man ( catch) ........... any fish yet

4. Could you be quite, please ? I ( listen)........... to the radio

5. How many times he (call) ............since he came to New York?

6. where your father (be) ............ since 1999

7. If the boy (eat) ........ the waste food , he (be) ...........ill

8. It (not rain) .............. the next day If the sky ( be)................ red in the evening

9. How long you (learn) .............. English?

10. Ngoc ever (love)...............him

REWRITE THE SENTENSES

1. I last saw Henry on Monday

=> I haven't ............................................

2. The last time it rained was 2 weeks ago

=> It hasn't...................................................

3. The last time he played video game was two hours ago

=> He ....................................................

4. The children haven't cleaned their classroom since last Monday

=> The last ..............................................

5. The last time she wrote to me was last month

=> She ......................................................