Lời giải:

Đặt $7p+1=a^3$ với $a$ là số tự nhiên.

$\iff 7p=a^3-1=(a-1)(a^2+a+1)$

Đến đây có các TH: 

TH1: $a-1=7;a^2+a+1=p$

$\Rightarrow a=8;p=73$ (tm) 

TH2: $a-1=p,a^2+a+1=7$

$\Rightarrow a=2$ hoặc $a=-3$

$\Rightarrow p=1$ hoặc $p=-4$ (không thỏa mãn) 

TH3: $a-1=7p;a^2+a+1=1$ (dễ loại) 

TH4: $a-1=1;a^2+a+1=7p$ (cũng dễ loại)

đây mới đúng

EXERCISE 9 : Change the active into the passive :
1 . The waiter brings me this dish

=> I am brought this dish by the waiter
2. Our friend send these postcards to us

=> These postcards are sent to us by our friend
3 . Their grandmother told them this story when they visited her last week

=> They were told this story by their grandmother when they visited her last week
4 . Tim ordered this train ticket for his mother

=> This train ticket was ordered for his mother by Tim
5 . You didn't show me the speacial camaras

=> I wasn't showed the special cameras
6 . She showed her ticked to the airline agent

=> Her ticked was showed to the airline agent
7.He lends his friend his new shoes.

=> His friend was lent his new shoes
8 . She left her relatives five milion pounds

=> Her relatives were left 5 million pounds
9 The shop assistant handed these boxes to the customer

=> These boxes were handed to the customer by the shop assistant
10 . The board awarded the first prize to the reporter

=> The first prize was awarded to the reporter by the board

sorry nhầm

EXERCISE 9 : Change the active into the passive :
1 . The waiter brings me this dish

=> I am brought this dish by the waiter
2. Our friend send these postcards to us

=> These postcards are sent to us by our friend
3 . Their grandmother told them this story when they visited her last week

=> They were told this story by their grandmother when they visited her last week
4 . Tim ordered this train ticket for his mother

=> This train ticket was ordered for his mother by Tim
5 . You didn't show me the speacial camaras

=> I wasn't showed the special cameras
6 . She showed her ticked to the airline agent

=> Her ticked was showed to the airline agent
7 . When will he lend his friend his new shoes ?

=> When will his friend be lent his new shoes?
8 . She left her relatives five milion pounds

=> Her relatives were left 5 million pounds
9 The shop assistant handed these boxes to the customer

=> These boxes were handed to the customer by the shop assistant
10 . The board awarded the first prize to the reporter

=> The first prize was awarded to the reporter by the board