1. đổi 59kj=59000j

nhiệt lượng thu vào của kim loại đó là : Q= m.c.\(\Delta\)t

=>c=\(\dfrac{Q}{m.\Delta}\)=>c =\(\dfrac{59000}{5.\left(50-20\right)}\)\(\approx\)393(j/kg.k)

vậy nhiệt dung riêng của kim loại đó là 393 và kim loại đó là đồng

2. nhiệt độ tăng lên của nước là

\(\Delta\)t=\(\dfrac{18000}{2,5.4200}.\)\(\approx\)1,7

vậy nước tăng thêm 1,7⁰C

Mark the letter A, B, C, or D on your answer sheet to indicate the word whose underlined part differs from the other three in pronunciation in each of the following questions.

A. takes

B. laughs

C. volumes

D. develops 

a, ta có Bx // AC

=> góc BNM =góc MAC( so le trong )

xét tam giác BMN và CMA ,có :

góc BMN =góc CMA (đối đỉnh )

góc BNM =góc MAC (chứng minh trên)

=>tam giác BMN =tam giác CMA

b, do 2tam giác AMC =NMB( theo câu a)

=>\(\dfrac{BA}{AC}\)=\(\dfrac{MN}{AM}\)(1)

TA CÓ :AN là tia pg góc BÁC =>góc BAM = góc MAC

mà góc BNM = góc MAC ( chứng minh trên )

=>góc BNM = góc BAM

=>tam giác BAN cân tại B

=>BN =BA =>\(\dfrac{BA}{AC}\)= \(\dfrac{BN}{AC}\)(2)

Từ (1) và (2) =>\(\dfrac{BA}{AC}\)= \(\dfrac{MN}{AM}\)(ĐPCM)

c, ta có BN //AC

mà NP vuông góc với AC

=>BN vuông góc với NP

Xét tứ giác ABNP có 3 góc BNP=NPA =PAB=90⁰

=>ABNP là hcn

mà hcn ABNP có BN =AB (vì tam giác ABN cân tại B)

=>ABNP là hình vuông =>BN =NP =AP=AB=6

Ta có :AP+PC =AC =>PC =8-6=2

xét tam giác PIC có PC //BN (do ac//bn)

=>\(\dfrac{BN}{PC}\)=\(\dfrac{NI}{IP}\)=\(\dfrac{BI}{IC}\)( theo hệ quả của định lí TA -LET)(3)

=>\(\dfrac{IN}{IP}\)=\(\dfrac{6}{2}\) =>\(\dfrac{NI}{NP-NI}\) =\(\dfrac{6}{2}\)=> 6(NP-NI)=2NI=>36-6NI=2NI

=>36=2NI+6NI => 36=8MI =>NI=4,5

ta có NP=NI+IP =>PI=6-4,5=1,5

Áp dụng định lí Py -ta go vào tam giác BIN

=> BI²=BN²+NI²=>BI²=6²+4,5²=56,25 =>BÍ=7,5

Ta có \(\dfrac{BI}{IC}\)=\(\dfrac{BN}{PC}\)=>\(\dfrac{BI}{IC}\)=\(\dfrac{6}{2}\) =>IC =\(\dfrac{BI.2}{6}\)=>IC=2,5

Vậy IC=2,5 ;BI=7,5 ; NI=4,5 ;IP=1,5

Read the following passage and mark the letter A, B, C, or D on your answer sheet to indicate the correct answer for each of the questions

Humans have struggled against weeds since the beginnings of agriculture. Marring our gardens is one of the milder effects of weeds – any plants that thrive where they are unwanted. They clog waterways, destroy wildlife habitats, and impede farming. Their spread eliminates grazing areas and accounts for one-third of all crop loss. They compete for sunlight, nutrients, and water with useful plants.

The global need for weed control had been answered mainly by the chemical industry. Its herbicides are effective and sometimes necessary, but some pose serious problems, particularly if misused. Toxic compounds threaten animal and public health when they accumulate in food plants, groundwater, and drinking water. They also harm workers who apply them.

In recent years, the chemical industry has introduced several herbicides that are more ecologically sound. Yet new chemicals alone cannot solve the world‟s weed problems. Hence, scientists are exploring the innate weed-killing powers of living organisms, primarily insects and microorganisms.

The biological agents now in use are environmentally benign and are harmless to humans. They can be chosen for their ability to attack selected targets and leave crops and other plants untouched. In contrast, some of the most effective chemicals kill virtually all the plants they come in contact with, sparing only those that are naturally resistant or have been genetically modified for resistance. Furthermore, a number of biological agents can be administered only once, after which no added applications are needed. Chemicals typically must be used several times per growing season.

Question:Which of the following best describes the organization of the passage?

A. Two possible causes of a phenomenon are compared.

B. A problem is described and possible solutions are discussed.

C. A general idea is introduced and several specific examples are given.

D. A recommendation is analysed and rejected

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