Ta có :

\(\left(a+b+c\right)\left(a+b+c\right)-2\left(ab+bc+ca\right)\)

\(=a^2+ab+ac+ba+b^2+bc+ca+cb+c^2-2ab-2bc-2ca\)

\(=\left(a^2+b^2+c^2\right)+\left(ab+ac+ba+bc+ca+cb-2ab-2bc-2ca\right)\)

\(=a^2+b^2+c^2\)

\(\left(a+b+c\right).\left(a+b+c\right)-2.\left(a.b+b.c+c.a\right)\)

\(=a^2+b^2+c^2-\left(2ab+2bc+2ca\right)\)

\(=a^2+b^2+c^2-2ab-2bc-2ca\)

\(=a^2-2ab+b^2-2bc+c^2-2ca\)

\(=\left(a-2b\right)a+\left(b-2c\right)b+\left(c-2a\right)c\)

Chúc bn học tốt

\(\text{(a+b+c).(a+b+c)-2(a.b+b.c+c.a}\)

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

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

\(=a^2+b^2+c^2\)

Vậy.......

Học tốt!

a: -21/39 rút gọn bằng-7/13

b;-7/13; -42/78

chứng minh cái gì vậy bạn ???

a)\(x^3y+3x^2y\)

b)\(-24x^2+4xy\)

a)  A=x^2+4x+4=(x+2)^2.

Giờ ta tính giá trị của đa thức A với x=98:

A=(98+2)^2=100^2=10000

b)  B=x^3+9x^2+27x+27=(x+3)^3.

Thế x=-103 => (-103+3)^3=-1000000

c) Tách C = a⋅b−a⋅c+2⋅c−2⋅b rồi kết hợp lại thành C=(a−2)⋅b+(2−a)⋅c.

Thế a,b,c vào được vậy 

C=(2−2)⋅1.007+(2−2)⋅(−0.006) =0

d) Bài này khó quá mà tui nghĩ là đưa mấy cặp (2023^2-2022^2) thành dạng a^2-b^2=(a-b)(a+b) á

d: D=(2023^2-2022^2)+(2021^2-2020^2)+...+(3^2-2^2)+(1^2-0^2)

=2023+2022+...+3+2+1+0

=2023*2024/2=2047276

a) Ta có: \(M=\left(\dfrac{1}{2}x^2y\right)\cdot\left(\dfrac{2}{3}xy\right)^2\)

\(=\dfrac{1}{2}x^2y\cdot\dfrac{4}{9}x^2y^2\)

\(=\dfrac{2}{9}x^4y^3\)

b) Hệ số là \(\dfrac{2}{9}\)

Phần biến là \(x^4;y^3\)

c) Bậc là 7

d) Thay x=-1 và y=2 vào M, ta được:

\(M=\dfrac{2}{9}\cdot\left(-1\right)^4\cdot2^3=\dfrac{2}{9}\cdot8=\dfrac{16}{9}\)

Nghe An Province was badly affected again when a typhoon hit the area last night. The storm began at around 11 p.m. and raged thoughout the night. Dozens of people were seriously injured and hundreds of others were left homeless. The severe winds caused extensive damage to property, including homes and businesses, particularly in Cua Lo, a coastal town in Nghe An. The storm had already weakened by the time emergency workers arrived in the area. Rescue operations have started and many people trapped in collapsed or damaged buidings have been freed. Workers are now clearing up the debris left behind by the severe storm. The government has already sent rescue equipment to Nghe An, as well as food and medical supplies. People left homeless have been taken to safe areas, where temporary accommodation will be built to house them. The weather bureau has issued flood warning for Nghe An and nearby provinces as heavy rain is expected to continue over the next few days

ban tham khao rtoi lam nha!

xin lỗi tui ngu anh lắm :)