Question

Answer 1

Bài 25: 

a: \(\left(a+b+c\right)^2=a^2+b^2+c^2+2ab+2bc+2ac\)

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

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

Answer 2

Bài 23:

a: \(\left(a-b\right)^2=\left(a+b\right)^2-4ab\)

\(=7^2-4\cdot12=1\)

b: \(\left(a+b\right)^2=\left(a-b\right)^2+4ab\)

\(=20^2+4\cdot3=412\)

Answer 3

Bài 21:

a: \(9x^2-6x+1=\left(3x-1\right)^2\)

b: \(\left(2x+3y\right)^2+2\left(2x+3y\right)+1=\left(2x+3y+1\right)^2\)