Bài 3:
e) \(x^2+2xy+y^2=\left(x+y\right)^2\)
f) \(a^2-2ab+b^2=\left(a-b\right)^2\)
g) \(y^2-1=\left(y-1\right)\left(y+1\right)\)
h) \(1-6x+9x^2=\left(3x-1\right)^2\)
Bài 4:
a) \(=x^2+4x+4-x^2+6x=10x+4\)
b) \(=x^2-2x+1-x^2+5x-6=3x-5\)
c) \(\left(a-b\right)^2+a\left(a+2b\right)=a^2-2ab+b^2+a^2+2ab=2a^2+b^2\)
d) \(=a^2+4ab+4b^2-3ab-3b^2=a^2+ab+b^2\)
\(3,\\ e,=\left(x+y\right)^2\\ f,=\left(a-b\right)^2\\ g,=\left(y-1\right)\left(y+1\right)\\ h,=\left(1-3x\right)^2\\ 4,\\ a,=x^2+4x+4-x^2+6x=10x+4\\ b,x^2-2x+1-\left(x^2-5x+6\right)=3x-5\\ c,=a^2-2ab+b^2+a^2+2ab=2a^2+b^2\\ d,=a^2+4ab+4b^2-3ab-3b^2=a^2+ab+b^2\)
