Ta có :

3x + y - 2x = 14

x : y : z = 3 : 8 : 5 hay \(\frac{x}{3}=\frac{y}{8}=\frac{z}{5}\)

Áp dụng tính chất dãy tỉ số bàng nhau , ta có :

\(\frac{x}{3}=\frac{y}{8}=\frac{z}{5}=\frac{3x}{9}=\frac{2z}{10}=\frac{3x+y-2z}{9+8-10}=\frac{14}{7}=2\)

\(\Rightarrow\hept{\begin{cases}x=2.3=6\\y=2.8=16\\z=2.5=10\end{cases}}\)

TL

Có:

x3=y8=z5=3x9=2z10

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

x3=y8=z5=3x9=2z10=3x+y−2z9+8−10=147=2

x3=2⇒x=6x3=2⇒x=6

y8=2⇒y=16

z5=2⇒z=10

HT

no I don't know

Ex1. Find the word which has a different sound in the part underlined. Read the words aloud

1.  A. volunteer           B. committee         C. guarantee                          D. degree

2.  A. chemistry          B. chemical            C. charity                              D. mechanic

3.  A. architect            B. church               C. childhood                         D. change

4.  A. collage               B. cave                   C. cycle  D. cancel

5.  A. child                  B. provide              C. mind  D. think

Ex 2. Find which word does not belong to each group.

     1.  A. environment      B. bank                  C. community                       D. neighbourhood

     2.  A. students             B. homework         C. blood        D. tutors

     3.  A. orphan               B. grandparents      C. nursing home D. elderly

     4.  A. rubbish              B. donate                C. collect                               D. money

     5.  A. green                 B. trees                   C. plant  D. collect

Ex3.   Choose A, B, C or D for each gap in the following sentences

     1.  He ate a lot of fried food so he              fat quickly.

          A. get                     B. got                     C. gets    D. will get

     2.  The Japanese eat a lot offish and healthy food,         they live for a long time.

          A. so                      B. because              C. or  D. but

     3.  Lan               English for more than a year but she can speak it very well.

          A. learns                 B. learn                  C. learned                              D. has learned

     4.  You should watch less TV because looking at screens in a long time    your eyes.   

A. hurt         B. hurts        C. is hurting         D. to hurt

     5.  Go Green               people to recycle rubbish, such as glass, cans and paper.

          A. to encourage      B. encourage          C. encouraged                       D. has encouraged

     6.  Be a Buddy has                 education for street children.

          A. given                 B. spent                  C. provided                           D. helped

     7.  He                 books for poor children for years.

          A. has collected     B. collects              C. is collecting                         D. collected

     8.  Linh often uses her headphones when she listens to music                       her parents don’t loud noise.     

A. so          B. but C. because   D. and

     9.  Ngoc loves              outdoors with trees and flowers.

          A. to be                  B. be                      C. being       D. A & C

     10. I think 10 years from now more people                     going to work by bicycle.

                     A. to enjoy   B. will enjoy          C. enjoying  D. enjoy

Ta có : 

\(\frac{a}{6}=\frac{b}{-4}\)

\(\text{Hay }\frac{a+b}{6+\left(-4\right)}\)

\(\Rightarrow\frac{a^2+b^2}{6^2+\left(-4\right)^2}=\frac{5}{20}=\frac{1}{4}\)

\(\frac{a^2+b^2}{6^2+\left(-4\right)^2}=\frac{1}{4}\Rightarrow\frac{a^2+b^2}{6^2+\left(-4\right)^2}=\frac{1}{2}\)

\(\Rightarrow\hept{\begin{cases}\frac{a}{6}=\frac{1}{2}\Rightarrow a=\pm3\\\frac{b}{-4}=\frac{1}{2}\Rightarrow b=\mp2\end{cases}}\)

Kẻ tia Md // BA ( hình vẽ ) => Md // CD ( do AB // CD )

Khi đó ta có :

\(\widehat{B}+\widehat{M_1}=180^o\left(\text{2 góc trong cùng phía}\right)\)

\(\Rightarrow140^o+\widehat{M_1}=180^o\Leftrightarrow\widehat{M_1}=40^o\)

Lại có : 

\(\widehat{M_1}+\widehat{M_2}=80^o\Rightarrow40^o+\widehat{M_2}=80^o\Leftrightarrow\widehat{M_2}=40^o\)

Lại có :

\(\widehat{M_2}+\widehat{D}=180^o\)\(\Rightarrow40^o+\widehat{D}=180^o\Leftrightarrow\widehat{D}=40^o\)