Bài 1
a, (x+1/2y)²=x²+2xy+1/4y²
b,(2x-1/3)²=4x²-4/3x+1/9
c,(x²+2y³)²=$x^{4}$ +4x²y³+4$y^{6}$
d,(x+3y)(x-3y)=x²-9y²
e,(1/3x+2y)(1/3x-2y)=1/9x²-4y²
f,(x+y+1)²=(x+y)²+2(x+y)+1=x²+2xy+y²+2x+2y+1
Bài 2:
a,31²=(30+1)²=30²+2.30+1²=900+60+1=961
b,59²=(50+9)²=50²+2.50.9+9²=2500+900+81=3481
c,101²=(100+1)²=100²+2.100+1²=10000+200+1=10201
d,36²-26²=(36-26)(36+26)=10.62=620
e,28.32=(30-2)(30+2)=30²-2²=900-4=896
Bài 3:
a,a²+6ab+9b²=(a+3b)²
b,1/9x²-2/3xy+y²=(1/3x-y)²
c,x²-x+1/4=(x-1/2)²