C1: (xy-1)(xy+5)=
a,x^2y^2+4xy-5 b,x^2y^2+4xy+5
c,xy-4xy-5 d,x^2y^2-4xy-5
C2: (x^2-2x+1)(x-1)=
a,x^2-3x^2+3x-1 b,x^2+3x^2+3x-1
c,x^3-3x^2+3x-1 d,x^3+3x^2-3x-1
C3: (x+3)(x^2-3xx+9)=
a,x^3-3^3 b,x-9 c,x^3+27 d,(x+3)^3
Đáp án:
Giải thích các bước giải:
`1)(xy-1)(xy+5)=x^2y^2+4xy-5`
`->B`
`2)(x^2-2x+1)(x-1)=x^3-3x^2+3x-1`
`->C`
`3)(x+3)(x^2-3x+9)=x^3+3^3=x^3+27`
`->C`
c1. a
c2. c
c3. c