bài 1 : tính
a) (5-xy)2
b) (3-2y)2
c) (3+x2) . (3-x2)
d) (5x-2y).( 25x2+10xy+4y2)
e) (3x+y). (9x2-3xy+y2)
g) (2x-1)3
bài 2 : viết các biểu thức sau về dạng tích
a) x2-2x+1
b) 4x2+12x+9
c) x3-27
d) 8x3+1
e) 4x2-1
g) x3-9x2+27x-27
h) x3+6x2+12x+8
bài 3 : rút gọn
a) ( x+3)2-(x-1)2
b) (3x+2).(3x-2)-9.(x+2).(x-2)
c) (x-3).(x2+3x+9)-(x3-5)
d) (x+1)3-x2(x+2)
e) (4x+y).(16x2-4xy+y2)-(4x-y).(16x2+4xy+y2)
\(\left(5-xy\right)^2=25-10xy+x^2y^2\)
\(\left(3-2y\right)^2=9-12y+4y^2\)
\(\left(3+x^2\right)\left(3-x^2\right)=9-x^4\)
\(\left(5x-2y\right)\left(25x+10xy+4y^2\right)=\left(5x-2y\right)\left(5x+2y\right)=25x^2-4y^2\)\(\left(3x+y\right)\left(9x^2-3xy+y^2\right)=\left(3x+y\right)\left(3x-y\right)=9x^2-y^2\)
