a: Xét (O) có 

ΔACB nội tiếp

AB là đường kính

Do đó: ΔACB vuông tại C

Xét tứ giác CEHF có 

\(\widehat{CEH}=\widehat{CFH}=\widehat{FCE}=90^0\)

Do đó: CEHF là hình chữ nhật

tungsten?

76. If you don’t want to get lost, you should bring a ……………. with you.

          A. torch               B. camera            C. compass          D. plaster

     77. The islands in Ha Long Bay are named ……………. things around us.

          A. in                     B. at                     C. on                    D. after

     78.London, the capital city of England, is a …city with many old buildings and beautiful parks.

          A. biggest             B. bigger              C. historic            D. history

     79.  Peach blossoms and apricot blossoms are my favorite …………….      

          A. food                B. flowers            C. fruits               D. trees

     80.         This type of machine is ……………. economical than that one.

          A. much               B. more                C. most                D. the most

76. If you don’t want to get lost, you should bring a ……………. with you.

          A. torch               B. camera            C. compass          D. plaster

     77. The islands in Ha Long Bay are named ……………. things around us.

          A. in                     B. at                     C. on                    D. after

     78.London, the capital city of England, is a …city with many old buildings and beautiful parks.

          A. biggest             B. bigger              C. historic            D. history

     79.  Peach blossoms and apricot blossoms are my favorite …………….      

          A. food                B. flowers            C. fruits               D. trees

     80.         This type of machine is ……………. economical than that one.

          A. much               B. more                C. most                D. the most

Lỗi ảnh, cập nhật lại nhé!

\(\dfrac{x+2}{3}=\dfrac{y-5}{-4}=\dfrac{z+1}{5}\Rightarrow\dfrac{2x+4}{6}=\dfrac{3y-15}{-12}=\dfrac{z+1}{5}\)

Áp dụng tính chất dãy tỉ số bằng nhau ta có:
\(\dfrac{2x+4}{6}=\dfrac{3y-15}{-12}=\dfrac{z+1}{5}=\dfrac{2x+4-3y+15+z+1}{6-\left(-12\right)+5}=\dfrac{\left(2x-3y+z\right)+\left(4+15+1\right)}{23}=\dfrac{72+20}{23}=\dfrac{92}{23}=4\)

\(\dfrac{x+2}{3}=4\Rightarrow x+2=12\Rightarrow x=10\\ \dfrac{y-5}{-4}=4\Rightarrow y-5=-16\Rightarrow y=-11\\ \dfrac{z+1}{5}=4\Rightarrow z+1=20\Rightarrow z=19\)

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

\(\dfrac{x+2}{3}=\dfrac{y-5}{-4}=\dfrac{z+1}{5}=\dfrac{2x-3y+z+4+15+1}{2\cdot3-3\cdot\left(-4\right)+5}=\dfrac{92}{23}=4\)

Do đó: x=10; y=-11; z=4

\(\dfrac{x+2}{3}=\dfrac{y-5}{-4}=\dfrac{z+1}{5}\text{ và }2x-3y+z=72\)

\(\text{Áp dụng tính chất dãy tỉ số bằng nhau:}\)

\(\dfrac{x+2}{3}=\dfrac{y-5}{-4}=\dfrac{z+1}{5}=\dfrac{2\left(x+2\right)-3\left(y-5\right)+z+1}{2.3-3.\left(-4\right)+5}=\dfrac{92}{23}=4\)

\(\Rightarrow\dfrac{x+2}{3}=4\Rightarrow x+2=12\Rightarrow x=10\)

\(\dfrac{y-5}{-4}=4\Rightarrow y-5=-16\Rightarrow y=-11\)

\(\dfrac{z+1}{5}=4\Rightarrow z+1=20\Rightarrow z=19\)

Gợi ý bạn đặt x y và giải hệ ra nhé

11. Mary loves _____ flowers.

A. a            B. an          C. the                   D. x

12. Jill went to ______ hospital to see her friend.

A. x            B. the                   C. a             D. an

13. Sandra works at a big hospital. She’s _______.

A. nurse     B. a nurse  C. the nurse         D. an nurse

14. She works six days _____ week.

A. in           B. for                   C. a             D. x

15. ______ is a star.

A. Sun                 B. A sun    C. The sun D. Suns

16. What did you have for ______ breakfast this morning.

A. x            B. a             C. an          D. the

17. London is _____ capital of England.

A. an          B. a             C. x            D. the

18. When ______ invented?

A. was telephone         B. was the telephone   C. were telephones      D. were a telephone

19. We visited _______ two years ago.

A. Canada and the United States             B. the Canada and the United States

C. the Canada and United States             D. Canada and United States

20. Are you going away next week? No, _______ week after next week.

A. a            B. the                   C. some      D. x

11.D

12. B

13. B

14. C

15. C

16. A

17. D

18. B

19. A

20. B

\(\dfrac{-5}{x}=\dfrac{15}{21}\\ \Rightarrow x=-5:\dfrac{15}{21}\\ \Rightarrow x=-7\)