Đáp án + Giải thích các bước giải:
Bài `1` :
a, `(7x+4)^2-(7x+4)(7x-4)`
`= 49x^2 + 56x + 16 - 49x^2 + 16`
`= (49x^2-49x^2) + 56x + (16+16)`
`= 56x + 32`
b, `8x(x-2)-3(x^2-4x-5)-5x^2`
`= 8x^2-16x-3x^2+12x+15-5x^2`
`= (8x^2-3x^2-5x^2) - (16x-12x) + 15`
`= -4x + 15`
c, `(x+1)^2 - (x-1)(x^2+x+1)-3x(x+1)`
`= x^2+2x+1-x^3+1-3x^2-3x`
`= -x^3 + (x^2-3x^2) + (2x-3x) + (1+1)`
`= -x^3-2x^2-x+2`
Bài `2` :
a, `3xy-6xy^2`
`= 3xy(1-2y)`
b, `3x^3+6x^2+3x`
`= 3x(x^2+2x+1)`
`= 3x(x+1)^2`
c, `x^3-x^2+2`
`= x^3+x^2-2x^2+2`
`= x^2(x+1)-2(1-x^2)`
`= x^2(x+1)+2(1-x)(1+x)`
`= (x+1)[x^2+2(1-x)]`
`= (x+1)(x^2+2-2x)`
d, `x^2+4x+4-y^2`
`= x^2 + 4x - y^2 + 4`
`= (x+2)^2 - y^2`
`= (x+2+y)(x+2-y)`
