Đáp án:
Giải thích các bước giải:
Bài 2:
a, (7x-2y)²=(7x)²-2.7x.2y+(2y)²=49x²-28xy+4y²
b, 9x²-1=(3x)²-1²=(3x-1)(3x+1)
c, (x²+1)²=(x²)²+2.x².1+1²=$x^{4}$ +2x²+1
d, 4x²-4x+1=(2x)²-2.x.1+1²=(2x-1)²
e, (y-3x)(y+3x)=y²-(3x)²=y²-9x²
g, (2x+$\frac{1}{3}$ )²=(2x)²+2.2x.$\frac{1}{3}$ +($\frac{1}{3}$ )²=4x²+$\frac{4}{3}$ x+$\frac{1}{9}$
Bài 3:
a, 499²=(500-1)²=500²-2.500.1+1²=250000-1000+1=249001
b, 301²=(300+1)²=300²+2.300.1+1²=90000+600+1=90601
c, 45.55=(50-5)(50+5)=50²-5²=2500-25=2475
d, 95²=(100-5)²=100²-2.100.5+5²=10000-1000+25=9025
