Bài 21:
a) Ta có:
\(9x^2-6x+1=\left(3x-1\right)^2\)
b) Ta có:
\(\left(2x+3y\right)^2+2\left(2x+3y\right)+1=\left(2x+3y+1\right)^2\)
Đề bài tương tự là:
c)\(4x^2+4x+1=\left(2x+1\right)^2\)
d)\(x^2+x+\dfrac{1}{4}=\left(x+\dfrac{1}{2}\right)^2\)
Bài 23:
a: \(\left(a-b\right)^2=\left(a+b\right)^2-4ab\)
\(=7^2-4\cdot12=1\)
b: \(\left(a+b\right)^2=\left(a-b\right)^2+4ab\)
\(=20^2+4\cdot3=412\)
Bài 21:
a: \(9x^2-6x+1=\left(3x-1\right)^2\)
b: \(\left(2x+3y\right)^2+2\left(2x+3y\right)+1=\left(2x+3y+1\right)^2\)
