gọi ah là dường cao tam giác abc

Sabc= \(\frac{ah\cdot8}{2}\)

S tam giác mới=\(\frac{ah.\left(8+5\right)}{2}\)=\(\frac{13.ah}{2}\)

mà nếu cạnh bc tăng thêm 5 cm thi diện tích tam giác abc tăng thêm 15 cm2

=>\(\frac{13ah}{2}\)-\(\frac{8ah}{2}\)=15 

=>\(\frac{5ah}{2}\)=15 

\(\frac{ah}{2}\)=3

ah=6

=> Sabc=\(\frac{6\cdot8}{2}\)=24\(cm^2\)

kho hieu qua

bn ơi cho mk hỏi bn lm tiếng anh hay toán mà chủ đề là tiếng anh mà bài lại là toán vậy alo????

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I D C A B H M K

Bài làm:

Từ A kẻ đường vuông góc với DM cắt DM tại K

Mà AB // KH và AK // BH ( vì cùng vuông góc với DM ) ; góc AKH = 90 độ

=> ABHK là hình chữ nhật

=> AB = HK (1)

Δ ADK = Δ BCH ( c.h-g.n)

=> DK = HC

Mà DH = HM <=> DK + KH = HC + CM

=> KH = CM (2)

Từ (1) và (2) => AB = CM, mà AB // CM

=> Tứ giác ABMC là hình bình hành

=> BM = AC

Last summer, I went to Nha Trang beach with my family , it was such a memorable summer holiday. We went there by car , and when we nearly got there, from the far distance , I could see how wide and beautiful the beach was. The weather was so nice that made me want to run directly to the beach, enjoy the fresh air and clean water. There were a lot of people swimming , sunbathing, playing volleyball on the shore , and some children even built sand castles and flew kites .We stayed at Edele hotel whose service I found very satisfied and I had the chance to eat the sea food there , they were very delicious . I went to Vinpearl Land , Long Sơn pagoda,too .They were very wonderful. I felt very fun and happy because I also met many foreigners ,they were tourists and I had talked to them a lot . We stayed in Nha Trang for a week and the last day , I went to some gift shop near the beach to buy souvenir for my grandparents and my friends . When I came back home , I felt very happy but a little regretted because I wanted to stay there longer. I told my dad I d Nha Trang and I hoped we can go to Nha Trang again one summer .

LÀM

Last summer , my parents took me to Phu Quoc for a week . Phu Quoc - dubbed as Ngoc Island . Here the many species of birds , with unique dishes . And the people there as well . They are interesting . It is also known as the paradise of sunshine and wind . The week passed quickly , and it was time for me to go home . But I can not forget the funny and strange things that are only available in Phu Quoc . Heaven of sunshine and wind 

HỌC TỐT !!!

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1;2;3;4;5;6;7;8;9;10

Bg

|2x - 4| = 25 - 7y² 

Ta có |2x - 4| > 0

=> 7y² < 25

=> y² < \(\frac{25}{7}\)

=> y² < 3

=> y = -1 hay y = 0 hay y = 1

Nhận thấy |2x - 4| chẵn

=> 25 - 7y² chẵn

=> y lẻ

=> y = -1 hoặc y = 1

=> y² = 1

Thay vào:

|2x - 4| = 25 - 7.1

|2x - 4| = 25 - 7

|2x - 4| = 18

=> 2x - 4 = 18 hay -18

     2x       = 18 + 4 hay -18 + 4

     2x       = 22 hay -14

       x       = 22 : 2 hay -14 : 2

       x       = 11 hay -7

Vậy với y = -1 hay y = 1 thì x = 11 hay x = -7 

1+5+9+15+20+32+18+53+21+6=x+216

180=x+216

x+216=180

x=180-216

x=-36

vậy x=-36

180 = x + 216

x = 216 - 180

x = 36

1. \(A=\left(a+b\right)^2+\left(a+b\right)^2\)

\(\Leftrightarrow A=2\left(a^2+2ab+b^2\right)\)

\(\Leftrightarrow A=2a^2+4ab+2b^2\)

2. \(B=\left(a+b\right)^2-\left(a-b\right)^2\)

\(\Leftrightarrow B=\left(a+b+a-b\right)\left(a+b-a+b\right)\)

\(\Leftrightarrow B=2a.2b=4ab\)

1) \(A=\left(a+b\right)^2+\left(a+b\right)^2\)

\(A=a^2+2ab+b^2+a^2+2ab+b^2\)

\(A=2a^2+4ab+2b^2\)

2) \(B=\left(a+b\right)^2-\left(a-b\right)^2\)

\(B=a^2+2ab+b^2-a^2+2ab-b^2\)

\(B=4ab\)

a. 2x^2 ( 5x^3 - 4x^2 - 7xy + 1 )

= 10x^5 - 8x^4 - 14x^3y + 1

b. ( x - 5 ) ( x + 3 )

= x^2 + 3x - 5x - 15

= x^2 - 2x - 15

c. ( x - 1 ) ( x + 2 )

= x^2 + 2x - x - 2

= x^2 - x - 2

d. ( 2x + y ) ( 2x - y )

= 4x^2 - 2xy + 2xy - y^2

= 4x^2 - y^2

a) \(2x^2\left(5x^3-4x^2.g-7xy+1\right)\)

\(=10x^5-8x^4.g-14x^3y+2x^2\)

b) \(\left(x-5\right)\left(x+3\right)\)

\(=x^2+3x-5x-15\)

\(=x^2-2x-15\)

c) \(\left(x-1\right)\left(x+2\right)\)

\(=x^2+2x-x-2\)

\(=x^2+x-2\)

d) \(\left(2x+y\right)\left(2x-y\right)\)

\(=4x^2-y^2\)