Câu 1:
a)x2(5x3-x-6)=5x5-x3-6x2
b)(x2-2xy+y2).(x-y)=(x-y)2.(x-y)=(x-y)3
Câu 2:
a)y2+2y+1=y2+2y+12=(y+1)2
b)9x2+y2-6xy=(3x)2-6xy+y2=(3x-y)2
c)25a2+4b2+20ab=(5a)2+20ab+(2b)2=(5a+2b)2
d)x2-x+\(\dfrac{1}{4}\)=x2-x+(\(\dfrac{1}{2}\))2=(x-\(\dfrac{1}{2}\))2
Câu 4:
a)14x2y-21xy2+28x2y2=7xy(2x-3y+4xy)
b)27x3-\(\dfrac{1}{27}\)=27(x3-\(\dfrac{1}{729}\))
c)3x2-3xy-5x+5y=(3x2-3xy)-(5x-5y)=3x(x-y)-5(x-y)=(x-y)(3x-5)
d)x2-2xy+3x-6y=(x2-2xy)+(3x-6y)=x(x-2y)+3(x-2y)=(x-2y)(x+3)
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